Fossil Plants At The Chalk Bluff Hydraulic Gold Mine, California

Gold Rush hydraulickers uncovered abundant Eocene leaves and petrified wood

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The Field Trip

While conducting research on the many interesting fossil plant localities in Northern California, I happened to read about an especially promising site in the fabulous Gold Rush Country, western foothills of the Sierra Nevada--the Chalk Bluff area, a number of miles from Grass Valley/Nevada City (they are contiguous communities in Nevada County).

The Chalk Bluff region was the scene of extensive hydraulic gold recovery operations during the mid to late 1800s, an historic period when miners extracted millions of dollars' worth of gold (mostly at the old price of around 20 dollars per ounce) from the widely exposed auriferous gravels of the northern Mother Lode.

In California, hydraulic mining initially began on a small scale in 1852, but soon developed into a regionally ubiquitous, sophisticated method of working great volumes of gold-bearing gravels. The basic idea was to aim high-powered jets of water through huge nozzles at the auriferous gravels, washing away tons upon tons of debris, after which the gold-bearing debris/sludge traveled through a deep cut or tunnel that was lined with a series of sluices to capture the gold. During roughly a 30-year period, from 1855 to 1884, hydraulic miners washed away approximately 250 million cubic yards of material. This created repeated catastrophic flooding of farmlands and valuable property in the flatlands below the hydraulic operations. Eventually, a farmer in Marysville by the name of Woodruff decided to sue the North Bloomfield Gravel Mining Company to prevent further debris from being discharged into the Yuba River. That case was presided over by Judge Lorenzo Sawyer, who issued his famous "Sawyer Decision" in January of 1884--a 225-page document that with effective legal decree abolished large-scale hydraulic operations in California for all time.

During the decades of gold extraction, the hydraulickers at Chalk Bluff incidentally exposed a wonderful fossil plant-bearing horizon interbedded with the auriferous gravel deposited by the Tertiary Yuba River (sedimentary accumulations usually considered a proximal correlative stratigraphic manifestation of the distal Eocene Ione Formation, whose type locality lies in the vicinity of Ione, Amador County, western foothills of the Sierra Nevada, about 62 miles southwest), a relatively narrow zone of fine-grained clays, usually not more than 3 feet thick, situated within the roughly 400 feet of pebble-cobble gold-bearing gravels of early middle to middle Eocene geologic age, some 48 to 45 million years old. This fossilferous bed of claystone--typically referred to as "chocolate shales" for their memorable coloration upon fresh exposure--contains the remains of numerous species of ancient botanic specimens: leaves and seeds and pollens and flowering structures, whose preservation is often magnificent. Sometimes the leaves reveal beautiful examples of the original cuticle, which is that thin wax coating on the upper epidermis of leaves that helps protect against excessive water loss, mechanical injury, and fungal attack. In the middle Eocene chocolate shales, exposed by hydraulicking methods during gold recovery, the original cuticle is locally quite common, appearing as a thin wax paper-like material that easily peels off the matrix upon direct exposure to the air; for this reason, paleobotanists wrap it in tissue paper with urgent immediacy to prevent any loss of the invaluable substance--a genuine rarity in the fossil record. In addition to the fossil leaves, relatively common pieces of petrified wood can also be observed in the same general area, mainly from a gravelly channel a few feet below the leaf-bearing chocolate shales.

My personal research disclosed rather quickly that the Chalk Bluff region is frequently mentioned in the paleobotanical literature on the fossil floras of Northern California. It is in fact a renowned fossil-bearing district, among the first plant-yielding areas scientifically studied in California after hydraulic operations had exposed the leaf-petrified wood deposit in the mid 1800s.

Indeed, the history of paleobotanical and geological investigations pertaining to Chalk Bluff is quite extensive. A professor Josiah Dwight Whitney first mentioned the Chalk Bluff fossils in an article published in the first volume of Geology, early 1870s. They were later described in detail in a truly remarkable paper, Report of the Fossil Plants of the Auriferous Gravel Deposits of the Sierra Nevada by Leo Lesquereux, Memoirs of the Museum of Comparative Zoology at Harvard College, Volume 5, Number 2, 1878. Prior to the advent of cyber-technology (AKA, the Internet), where even the most obscure scientific papers can often be accessed online, I was fortunate to locate an original copy of Lesquereux's classic monograph at the library of the California Division of Mines and Geology in Pleasant Hill. Lesquereux includes numerous detailed line drawings of the fossil leaf specimens--a feature usually inferior to photographs, but in this example the scholarly drawings definitely enhance the quality of the finished product. In 1880, professor Whitney discusses the Chalk Bluff area once again in his monumental publication The Auriferous Gravels of the Sierra Nevada, California, Vol. 1, Memoirs of the Museum of Comparative Anatomy at Cambridge, Massechesetts.

In 1911, geologist Weldemar Lindgren published the definitive statement on the gold-bearing gravels of the northern Sierra Nevada: United States Geological Survey Professional Paper 73, The Tertiary Gravels of the Sierra Nevada of California. For a section of the volume entitled Tertiary Fossil Plants, Lindgren solicited a report from then leading paleobotanist F. H. Knowlton, who mentions the Chalk Bluff site, along with 12 additional plant-bearing localities in northern California, including: Washington Gravel Mine, Independence Hill near Iowa City in Placer County; Volcano Hill, Placer County; Monte Cristo Gravel Mine, "summit of Spanish Peak in Plumas County;" Mohawk Valley, Plumas County; Bowens Tunnel, along the North Fork of Oregon Creek near Forest City in Sierra County; "about seven and a half miles southwest of Susanville, Lassen County;" Table Mountain, Tuolumne County; the north end of Mountain Meadow, Lassen County; and "near Moolight," Lassen County.

In her 1935 report on a fossil leaf deposit in Plumas County, Northern California, Susan S. Potbury wrote that H. D. MacGinitie was, as that date, revising the Chalk Bluffs Flora, the results to appear in a forthcoming paleobotanical monograph. MacGinitie finally published his findings in 1941 in Carnegie Institute of Washington Publication 534, A Middle Eocene Flora from the Central Sierra Nevada. This is certainly the best study of the Chalk Bluffs Flora. "Mac" (an endearing moniker, given to him by contemporary professional paleobotany acquaintances) concluded that the Chalk Bluffs Flora could be assigned stratigraphically to the "Capay Stage" of the Eocene (named after the marine Capay Formation)--then understood as middle Eocene in geologic age--around 48 to 45 million years old--an interval that geologists currently correlate with the coal-bearing Domengine Formation exposed in the East San Francisco Bay area.

Of course, based on several independent lines of scientific evidence, Capay-age now refers to rocks of late early Eocene times, roughly 52 to 50 million years old. Still and all, "Mac" got it right. Unfortunately, in later years--even after detailed stratigraphic evaluations definitively proved that the Chalks Bluffs Flora is younger than the revised Capay age--numerous paleontology investigators continued to perpetuate the idea that that refined definition of Capay Stage (52 to 50 million years old--not the age "Mac" had in mind) still applied to the Chalk Bluffs Flora, which is younger at approximately 48 to 45 million years old.

As can best be determined, the Chalk Bluff leaf-bearing site is far from under-reported. It has been quite well known to amateur paleobotany enthusiasts since the 1860s, and several scientists have also spent considerable time investigating the fossil occurrence. As a matter of fact, the Chalk Bluff leaves that Leo Lesquereux first examined in the 1870s had been collected in the late 1860s by Charles D. Voy, an acclaimed naturalist and indefatigable gatherer of South Sea Islands ethnological items.

So imagine my frustration when I could not find in any of the listed references a single explicit description of the exact geographic position of the Chalk Bluff region. The most promising lead came from a generalized map of the Northern Mother Lode contained in the volume, Geologic History of the Feather River Country, California, by Cordell Durrell, 1987. Durrell's map placed Chalk Bluff somewhere between Nevada City and Colfax in Nevada County--a decent start, I'll admit--but the map lacked important side-roads roads leading directly to the area.

Now, normally, I'm not inclined to head off on a paleontology excursion without a full complement of accurate field information. But in this instance I was pretty much forced to do just that. If I was going to find the reportedly magnificent Chalk Bluff fossil field, I would necessarily need to head in to the hills impoverished in supporting directions data.

My plan of attack was pretty straightforward. I'd simply follow Interstate 80 east out of the Sacramento area (at that date, I had fortuitously been visiting Northern California on personal business unrelated to matters paleontological), then turn north at the first major road in Colfax, about 46 miles distant in the direction of Reno, Nevada. Along the way toward Nevada City from Colfax, I'd decided to strike out east at approximately the "correct" distance north of Colfax--all of this itinerary, mind you, dictated to me by that generalized map included in Cordell Durell's publication.

The plan was admittedly a long shot. I couldn't be sure I'd be able to recognize the Chalk Bluff region even if I were actually right on top of it. Additionally complicating the situation was that, based on previous journeys into that portion of the Gold Rush Country, I already understood that innumerable side roads presented a bewildering maze of routes that led to isolated communities and recent real estate developments--all part of the burgeoning populations of Nevada and Placer counties.

So, which path to take to the fossils? My general idea, of course, was to watch for telltale evidence of hydraulic mining; the middle Eocene fossil plants were associated with auriferous gravels exploited by open pit hydraulic methods during the mid to late 1800s. But unless I could happily choose the correct route right off, I might travel far afield of my destination, losing precious time that could have been devoted to paleobotanical explorations.

For this reason--and, simply because I had the hankering for it--I had decided to tote along a gold pan I'd borrowed from an acquaintance, in addition to my usual store of paleontological equipment. If I couldn't locate the Chalk Bluff fossil plant horizons within a decent amount of time, I figured I'd spend the remainder of my allotted day's adventures panning for gold along the famous Bear River, a known gold-producer of the 1800s. As a matter of fact, the so-called Colfax Quadrangle (within which Chalk Bluff and Bear River reside) yielded many millions of dollars' worth of gold during the Gold Rush delirium days, albeit the vast majority came from the hydraulic operations at Chalk Bluff.

By the time I made Auburn (33 miles east of Sacramento) in the early morning hours of a potentially blistering summer's day down in the Great Central Valley, I was ready for some breakfast--a propitious decision as it turned out. Maybe it was the strong bracing coffee, or perhaps the energizing nourishment provided by the bacon and eggs and biscuits but suddenly I began to think more clearly on my day's adventures. While gazing out the window of that coffee shop on the striking mixed conifer/oak woodland scenery of the western Sierran foothills, I happily concluded that I was not necessarily compelled to report to luck in order to locate the Chalk Bluff fossil plant bonanza. What if I could obtain a map of Nevada County? And what if that map showed the exact location of Chalk Bluff? This idea was definitely worth a try, I decided.

At the grocery store across the street I found a road atlas of California. So far, so good, I thought. The publication I'd come across had a positive reputation for reliability. Immediately I turned to Nevada County and scanned the page for any kind of conceivable clue--and then, there it was right before my eyes--all the information I needed to find Chalk Bluff. I purchased that road atlas on the spot, and the rest as they say is history.

It's probably problematic whether I would have been able to locate Chalk Buff without the aid of that road atlas, but at least I'm comforted to realize that I intuitively had the correct idea: Head north out of Colfax along the first major road I came to.

Speaking of Colfax. Here's a geological aside to keep in mind: If you travel about 9 miles further on up the freeway from Colfax (roughly a mile past the Gold Run rest stop), you'll encounter along the north (left) side of I-80 one of the most accessible and extensive sections of unexploited middle Eocene auriferous gravels yet remaining in all of Northern California; it's the spectacular roadcut that extends roughly a half mile along I-80, a cut that gives travelers a wonderful opportunity to view up close and personal, from a moving vehicle, the excellently preserved fossil thalwegs of a river that dropped unimaginable fortunes in gold.

A few miles north of Colfax, by the way, one crosses the Bear River. It was here that I decided to try my hand at a little gold panning during that initial visit to Chalk Bluff. On my return from the fossil plant horizon, I must have spent the better part of a couple of hours with bare feet in the Bear, rear on the bank and nose to the water, peering intently into the swirling material in my pan--all to no avail, ultimately.

That golden gleam eluded my sight, although I'm not in the least surprised. My gold panning technique is far from efficient. Perhaps this has to do with a woeful lack of practice, because it's not that I haven't tried to improve my gold recovery method. I once had a certified gold panning expert try to improve my ways. He repetitively dropped two or three pieces of lead shot into my successive pans of experimental gravel, then instructed me to recover those pieces by slowly and surely concentrating the "fines' of my dirt with waters supplied by a mountain stream. After I'd cost him a small fortune in lead, he concluded with high confidence that I'd likely become prolifically rich someday, as he was certain that I would have no trouble finding gold nuggets no smaller than a cannonball.

During that first visit to the Chalks Bluffs Flora deposit, I continued to follow the road atlas with faithful fidelity, managing to arrive at the great abandoned hydraulic pit in good order, with plenty of time available not only for fossil prospecting, but general geologizing, as well. As I quickly ascertained through reconnaissance, getting up to paleontological speed as it were, the fossil leaves and petrified wood occur to the immediate north and south of the primary dirt path through the middle Eocene auriferous gravels exposed by hydraulic gold miners during the mid to late 1800s.

I also noted, upon subsequent visits undertaken not a few years later, that one needs to watch carefully for No Trespassing signs here. Most of this area remains in private ownership, where explicit advance permission from the property owners must be secured prior to fossil hunting. And even if you don't observe obvious posted documentation of private property--never assume that one is allowed to step anywhere off the main road within the Chalk Bluff hydraulic mining region without advance approval. Always conduct preliminary due diligence: Contact officials with the local United States Forest Service office to determine the most up-to-date rules and regulations regarding fossil collecting at Chalk Bluff.

As you look to the north at the main Chalk Bluff fossiliferous sector, you will observe a broad ravine directly before you. Fossil leaves, seeds, flowering structures, and pollens occur in the pale brown-weathering shales near the base of the south side of that steep ravine--in other words, directly below your feet. When freshly exposed by hand excavation, the drab fossil-yielding shales instantly transform into a rich chocolate brown coloration--hence, their popular informal name "chocolate shales."

But before you begin to hunt for fossils along that northern side, step across the road and take in the vista that spreads to the south. Here you will observe great chasms sliced through the gold-bearing gravels--acre after acre of water-blasted land that yielded unfathomable fortunes in gold.

And now, only if unambiguous permission is still granted to collect here, proceed to find your way to the bottom of that ravine along the north side of the dirt road.

From that top-side vantage point, though, there appears to be no easy route to reach the fossil-bearing area. Most of this north-facing wall is way too steep to try to descend safely. It was exposed by the gold seeking hydraulickers of the mid to late 1800s when they laid bare mile after mile of the auriferous gravel throughout the northern Mother Lode Country. During my first visit to Chalk Bluff, I was so exhilarated about having reached the right area that I impatiently scrambled down the south side of that ravine, dangerously sliding most of the way. Subsequent visits proved that this method was not only unesthetic, but needlessly reckless as well. A much safer path the bottom exists a short way west of a convenient parking area, where the slopes remain far less precipitous and treacherous.

Once at the base of the hydraulic cut, watch carefully for the fine-grained fossiliferous layer of chocolate-colored material, the so-called chocolate shales. Although this horizon is relatively narrow within the exposed sedimentary section--it is only three feet thick at most (and often partially masked by eroding overburden)--the leaf-bearing rocks are so different in lithology from the reddish brown pebble-cobble saturated auriferous gravel that you should have little difficulty identifying it in the field. If in doubt, give any potential fossil-bearing strata a whack or two with a geology hammer, exposing fresh rock. The leaf-yielding claystone is so fossiliferous that almost any chunk exposed will reveal at least a few 48 to 45 million year-old plant remains on the surface.

The lithology of the fine-grained claystone, in combination with the abundance of fossil plants preserved within, provides persuasive evidence that the fossiliferous zone accumulated in stagnant oxbow lakes along the floodplains of Eocene-age aggrading rivers (watercourses that built up sediments, instead of downcutting their channels) that dropped great quantities of gold derived from now long-eroded lode veins in igneous rocks.

And make no mistake about it. This claystone horizon in the middle Eocene auriferous gravel is often amazingly fossiliferous; the carbonized leaf impressions frequently lie plastered across the bedding planes, crisscrossing in a fascinating design of exceptional preservation (so-called "leaf litter"). The fossil-bearing layer of "chocolate shales" occurs in the coarse gravels that lie stratigraphically above the older "inner channel," a relatively narrow zone only about 40 feet deep (on average) and tens of feet wide, situated near bedrock, within which the vast majority of the abundant gold recovered by hydraulic methods was concentrated. Above the inner channel, or "blue ground" as the miners referred to this unbelievably rich zone, the younger gravels accumulated to a thickness of approximately 400 feet. These "bench gravels" contained much lower concentrations of gold, although a few reported localities in the younger auriferous gravels did indeed yield prolific quantities of the precious metal. 

Of course, the popular term "auriferous gravel" is not a formally accepted geologic formation name. It has no strict nomenclatural significance because there are other gold-bearing gravels in California of different ages. But, through long usage and tacit acceptance by local California geologists, the phrase has come to connote a very specific rock deposit. The auriferous gravels accumulated approximately 48 to 38 million years ago during the Eocene Epoch of the Cenozoic Era, an epoch technically calibrated at 56 to 33.9 million years ago. Based on the traditional interpretation of the geologic evidence, the gravels were deposited along the flood plains of aggrading rivers (most famously, the Tertiary Yuba River)--that is, water courses which were building up sediments instead of eroding their channels.

One of the great mysteries confronting geologists who've studied the auriferous gravel is why rivers that for millions of years were eroding their channels would suddenly begin to aggrade, or build up sediments. Several explanations have been considered to account for this occurrence, but only two competing plausible models appear to offer possibilities to fulfill the equation, answer all the questions.

In his classic work Geologic History of the Feather River Country, geologist Cordell Durrell suggested that a prolonged change of climate from one of regular wet-and-dry seasons to one of irregular wet-and-wetter cycles may have triggered repeated episodes of catastrophic flooding, much like that which occurs in the vicinity of Rio De Janeiro, Brazil, a region with a climate and vegetation similar to that inferred for the Sierra Nevada area some 48 to 45 million years ago. Such floods are very local, of course, but Durrell pointed out that no single flood need cover a large area to account for the accumulation of auriferous gravel. All that was needed was to have a sufficient number of flooding episodes within every part of the region where auriferous gravels now occur--in other words, the 10 northern counties of the Sierra Nevada, or an area of roughly 12,000 square miles.

At first, this might seem to represent a prohibitively extensive area for floods to affect. But consider Durrel's calculations. Deposition of the auriferous gravel probably lasted for as long as 10 million years, or all of the middle Eocene. Therefore, there was ample time for periodic flooding to account for the gold-bearing gravels. Durrell suggested that if only one consequential flood occurred every 50 years, there could have been as many as 200,000 floods. If the rain gods were more generous and the figure was closer to one flood every 20 years, then the total climbs to a possible 500,000 floods.

Now, Durrell introduces us to some basic arithmetic. Suppose each flood deposited an average of only two feet of sediment affecting an area of 10 square miles (a conservative figure completely within reason). That would mean that it would require 250,000 floods to bury the 10 northern counties of the Sierra Nevada to a depth of 400 feet, the actual measured thickness of the auriferous gravels we see today in California.

An alternate, second, explanation was championed by the late paleobotanist/geologist Howard Schorn, former Collections Manager of Fossil Plants at the University California Museum of Paleontology. Schorn and others postulated that about 52 million years ago (early Eocene), the marine waters that had covered what's now California's Great Central Valley for several million years began to regress, or retreat. That drop in sea level caused streams flowing westward from the ancestral Sierra Nevada to begin to incise their channels. At around 48 million years ago (early middle Eocene), sea levels began to rise once again when the Domenguine-Ione Seaway re-flooded (transgressed) the proto-Great Central Valley, returning marine conditions to a terrestrial area previously left high and dry.

That rise in sea level began to block, or dam, the mouths of the ancient northern Sierra Nevada rivers, among them the Tertiary Yuba River, initially causing gold-rich sediments to accumulate in the moderately downcut inner channels (areas later known to hydraulickers as the fabulous "blue ground"). Continuing incremental sea level increases contributed to the deposition of progressively greater volumes of sedimentary material in the older eroded river courses, completely filling them, until at last the Tertiary Yuba River spread out over the floodplains in wide meandering curves, thus creating by aggradation the bench gravels and chocolate shales--within which the middle Eocene Chalk Bluffs Flora occurs.

Some 70 species of ancient plants have been identified from the Chalk Bluffs Flora (which refers collectively to the total aggregate of plants obtained from every locality in the middle Eocene auriferous gravels of California's Northern Mother Lode district), including such varieties as: American climbing fern; cinnamon fern; flowering fern (solely from pollen evidence); Mexican cycad; broadleaf lady palm; sarsaparilla vine; crack willow; swamp hickory; an extinct genus of Engelhardia, a tree whose modern types are native to northern India east to Taiwan, Indonesia and the Philippines; Formosan alder; a species of chinquapin now endemic to Vietnam and China; three extinct oaks similar to the living interior live oak, Sierra oak, and Japanese blue oak; Mexican elm; Breadfruit; Pea fig; an extinct fig; Yellow lotus (also called Yellow pond lily); Katsuna tree; a species of Hyperbaena resembling a variety now native to Central America; umbrella magnolia; two species of extinct Cinnamomum (Cinnamon trees); six species of evergreen laurels, including swampbay; Chinese hydrangea; American witch-hazel; American sweetgum (also called Liquidamber, now native to the southeastern United States, Mexico, and Central America); five species of extinct sycamores (one resembles the modern American sycamore), including the magnificent Magnititiea whitneyi (leaves can spread to 13 inches wide; it resembles the living sycamore Platanus lindeniana of east-central Mexico to Guatemala); Cocoplum; Slimleaf rosewood; a species of rosewood that resembles a kind now native to China; a species of Tick clover that is similar to a type now endemic to East Asia; a legume whose closest modern counterpart lives in the Amazon flooplains; Chinese olive; Tree of heaven; Cuban cedar; a spurge (Euphorbia) now endemic to southern Mexico and Central America; East Asian mallotus (also called the "food wrapper plant"); staff vine; a species of Phytocrene now native to Myanmar, Sumatra, Java, and the Philippines; Smooth sumac; an extinct maple that resembles the living Red maple and trident maple (now native to China); mallows (obtained only from pollens); a Cupania tree presently endemic to the South American countries--Argentina, Uruguay, Paraguay, Brazil, and Bolivia; a species of Thouinidium, a shrub to small tree now common in southern Mexico; a variety of Meliosma, a large brush to small tree, presently native to China; a species of Bridelia, a large shrub or small tree native to southeast Asia; walnut (only from pollens); two species of buckthorne now endemic to southeastern Asia and China; princess vine; Franklin tree; spicewood; black gum (also known as Black tupelo); Tropical almond; Pacific dogwood; American persimmon; black ash; oleander; milkwood; dog-strangling vine; a species of viburnum presently common to Mexico; a species in the genus Mikania, often called hempvine--it's native to Mexico, Central and South America, the West Indies, and the southeastern US; a species that most closely resembles the genus Tylophora, a vine native to tropical and subtropical Asia, Africa, and Australia; a type that most closely matches the genus Premna (mint family), a small tree or shrub common in tropical and subtropical regions of Africa, southern Asia, northern Australia, and several islands in the Pacific and Indian Oceans; a specimen that is quite similar to the extant nettlespurge; forms that most closely match the genus Croton, currently native to Indonesia, Malaysia, Australia, and the western Pacific Ocean islands; a mysterious extinct plant that shows characteristics of typical of both Blackjack oak and a sycamore; and the following conifers, all obtained only from palynological specimens blown in from great distances--pine, spruce, and fir.

All specimens are middle Eocene in geologic age, roughly 48 to 45 million years old--an awe-inspiring fossil flora whose overall composition resembles a modern subtropical Mexican Elm-Liquidamber forest at the foot of Mount Orizaba in Vera Cruz, Mexico, where rainfall averages 60 to 80 inches a year, and the usual year-round temperature is close to 65 degrees, with no frost. There are also similarities to such modern subtropical forests as those found along the Rio Moctezuma at Tomazunchale, Mexico; to the Liquidamber-Oak and Mexican Elm forests near Coban, Guatemala; and to the Liquidamber forests in the state of Morelos and the eastern Sierra Madre west of Tomazunchale, Mexico.

Today, the Chalk Bluffs Flora lies at elevations between 2,500 and and 4,000 feet amid what botanists variously categorize as the Transition Life zone, the Sierra Transition life zone, or the Sierran Lower Montane vegetation zone--an area within California's western Sierra Nevada foothills now dominated by a decidedly Mediterranean-style meteorology; that is to say, summers typified by rather high daytime temperatures (often exceeding 100 degrees), low humidity, and scant rainfall (usually as little as one inch for the entire three month period). Virtually all the effective precipitation occurs during wintertime--when temperatures can drop to 5 degrees Fahrenheit--as frequent heavy rains and occasional snow. It's a land characteristically populated by the following common plants: Azalea (Rhodendron occidentals); Big-leaf maple (Acer macrophyllum); Black cottonwood (Populus trilocarpa); Black oak; (Quercus kelloggii); Canyon live oak (Quercus chrysolepis); Chinquapin (Castanopis sempervirens); Chokecherry (Prunus demissa); Coffeeberry (Rhamnus rubra); Creambush (Holodiscus discolor); Deer brush (Ceanothus integerrimus); Dogwood (Cornus nuttallii); Douglas-fir (Pseudotsuga texifolia); Elk clover (Aralia californica); Gooseberry (Ribes roezlii); Hazelnut (Corylus rostrata); Incense cedar (Libocedrus decurrens); Knobcone pine (Pinus attenuata); Labrador tea (Ledum glandulosum); Madrone (Arbutus menzsiesii); Mahala nut (Ceanothus prostratus); Manzanita (Arctostaphylos patula); Mountain mahogany (Cercocarpus betuloides); Mountain misery (Chamaebatia foliosa); Pigeonberry (Rhamnus californica); Poison oak (Rhus Taxicodendron diveriloba); Red alder (Alnus rubra); Serviceberry (Amelanchier alnifolia); Sugar pine (Pinus lambertiana); Sumac (Rhus trilobata); Tan oak (Lithocarpus densiflora); Thimbleberry (Rubus parviflorus); Tobacco brush (Ceanothus velutinus); White fir (Abies concolor); Wild grape (Vitis californica); Wild rose (Rosa spp.); Willow (Salix spp.); and Yellow pine (Pinus ponderosa).

A major collecting convenience at Chalk Bluff is that the claystone is quite soft. This means that the fossilferous material is easily split with a geology hammer (chisels, optional), or perhaps a brick layer's wide blade tool--as advocated by not a few paleobotanists for all leafiferous localities, even though the tool obviously lacks the necessary punch/mass required to split the more indurated, hardened, leaf-bearing rocks; the upshot: a good old regular geology hammer is best for splitting virtually all leaf-bearing shales. The plants preserved in the chocolate shales have remained most life-like in preservational detail, despite the undeniable fact they've been buried for approximately 48 to 45 million years. Several specimens in my collection reveal actual original cuticle, which is that thin wax coating on the upper epidermis of leaves that helps protect against excessive water loss, mechanical injury, and fungal attack. In the middle Eocene chocolate shales, exposed by hydraulicking methods during 19th Century gold recovery, the original cuticle is locally quite common, appearing as a thin wax paper-like material that easily peels off the matrix upon direct exposure to the air; an invaluable substance (it could provide prehistoric DNA, for one)--a genuine rarity in the fossil record.

In addition to the paleontologically rewarding leaf-bearing chocolate shales, the Chalk Bluff district also yields locally obvious examples of petrified wood. It's of similar geologic age as the fossil leaves, middle Eocene, but the permineralized wood occurs primarily within auriferous bench gravel beds slightly older than the chocolate shales. Most of the sporadic concentrations of petrified woods lie north of the shale beds just explored for fossil leaves, where it erodes free of the brownish auriferous gravels as hand-sized specimens, mainly. Even though the wood is excellently silicified, replaced by the mineral silicon dioxide, the material is far from gem quality. It has not been agatized or replaced by the kinds of colorful minerals that might justify great lapidary value. Preservation of the woody structure is usually superb, though, so folks with slabbing saws just might want to try sectioning specimens to expose the growth lines.

In an historical perspective, petrified wood used to be quite abundant in the coarser auriferous gravel lenses during hydraulic mining days--including occasional spectacular occurrences of standing stone stumps and lengthy fallen logs. The old-time gold seekers removed great quantities of it while they blasted away entire mountainsides with their powerful jets of water, stacking the permineralized organic remains in sizable piles so that they would not interfere with gold extraction activities. Sometimes they used the larger rock logs to line their long flumes, employing with practical ingenuity a plentiful natural resource to help transport water to the operations. Today, petrified wood is only common to locally abundant in the many massive, abandoned surface mines scattered throughout the northern Mother Lode country--notably Buckeye Flat, Sailor Flat, Dutch Flat, North Columbia, Iowa Hill, and Malakoff Diggins--most of it having been carted away decades ago as curiosity pieces.

The petrified wood, leaves, seeds, flowering structures, and pollens preserved in the Chalk Bluffs Flora have figured quite prominently in a great geophysical and geomorphological debate: Just how high was the ancestral Sierra Nevada during the geologic past? The traditional view, famously championed by the late paleobotanist Daniel I. Axelrod (and numerous other scientists, of course), is that the Sierra Nevada, as we know it today, is a relatively recent topographic expression, uplifted to its present dramatic elevations mainly during the past five million years--with most of that uplift occurring over the last three million years. Yet, studies based on sophisticated geophysical evaluations of many mountain ranges, combined with paleobotanical leaf character analysis (study of leaf size, shape, venation, and percentage of entire to serrated margins, among other parameters, to help determine the paleoclimate and paleoelevation of a given fossil site), preliminarily suggested quite strongly that the Sierra Nevada, along with the neighboring ancestral Great Basin region, stood just as high if not higher during middle Eocene Chalk Bluff times than at present.

Finally, though, after analyzing multitudinous information amassed from disparate disciplines of scientific research, investigators seem to be gradually approaching a consensus--namely, that the ancestral central to southern Sierra Nevada existed during Eocene times as a relatively low-lying, gradual-gradient western slope to a high plateau region, the so-called Nevadaplano, that stretched eastward across present-day Nevada, an Eocene upland area that rose as high, if not higher, than the peak elevations seen there today. At around 16 million years ago, the Nevadaplano began to collapse, drop, through extensional geophysical strains associated with incipient formation of the Great Basin, eventually falling to roughly present-day elevations by about 13 million years ago.

Which would mean, ultimately, that the central to southern Sierra has indeed been dramatically uplifted during the past five million years or so. On the other hand, today's northern Sierran areas would have remained at around the same elevations as those that existed during deposition of the Eocene auriferous gravels some 48 to 38 million years ago. If that indeed turns out to be the case, everyone involved in the Sierran elevation studies can claim a partial victory: the grand solution to the Sierra Nevada Eocene elevation problem would involve a major compromise--around two-thirds of the Sierran length would have been greatly uplifted during the past five million years.

Today, at an elevation of roughly 3,000 feet, the Chalk Bluff fossil field is theoretically accessible to year-round exploration. Realistically, though, you'll probably wish to consider skipping a wintertime visit, due to the usual heavy rains and occasional snowstorms that effectively prohibit efficient and comfortable explorations. Also, if one calculates that one could possibly beat the invariable extreme summertime heat in California's Great Central Valley by fleeing to Chalk Bluff--forget it. The altitude there is just not sufficient to influence an appreciable daytime temperature reduction from "down below." The evenings and nights tend to range somewhat cooler, though, so that would constitute a positive meteorological condition. All in all, late spring (after the rainy season) and early to mid fall (before seasonal precipitation patterns) usually offer the most reliably comfortable conditions for hiking, for efficient paleobotanical investigations.

Access to the Chalk Bluff district is via a system of excellent asphalted surface streets and well-graded dirt roads. Most conventional vehicles in reliable operating condition should have no trouble reaching the fossiliferous area. The main dirt road in can turn treacherous during the rainy season, of course, especially if humungous logging rigs have rumbled through, transforming the route into a hazardous quagmire. Too, throughout the Sierra freezing season, be extra alert for "black ice" along the roads--patchy frozen invisible films that can send unsuspecting drivers into a panicked slide.

Today, the Chalk Bluff fossil locality lies amidst what botanists often call the Sierran Lower Montane vegetation zone, characterized by ponderosa pine, sugar pine, knobcone pine, willow, Black cottonwood, alder, manzanita, and madrone. Yet, during middle Eocene times some 48 to 45 million years ago, this very area would have held a stagnant oxbow lake within the vast floodplains of a meandering Amazon-like river, where countless leaves, seeds, flowering structures, and pollens from a subtropical forest fell into the gradually accumulating clays of oxygen-poor waters, preserving such plant life as palm, magnolia, swampbay, sarsaparilla vine, breadfruit, tupelo, fig, persimmon, cinnamon, sycamore, and liquidamber in amazing detail.

Images Of Fossils

A leaf from the extinct sycamore Macginitiea whitneyi, collected between 1933 and 1938 by paleobotanist H. D. Macginitie (who originally called the specimen Platanophyllum whitneyi) from the Chalk Bluff hydraulic gold mine, middle Eocene auriferous gravels, western foothills of California's Sierra Nevada. It resembles the living sycamore Platanus lindeniana of east-central Mexico to Guatemala. Photograph courtesy paleobotanist Diane M. Erwin.

A leaf from the extinct sycamore, now known as Macginitiea whitneyi, collected in the late 1860s by Charles D. Voy--acclaimed naturalist and indefatigable gatherer of South Sea Islands ethnological items--from the Chalk Bluff hydraulic gold mine, middle Eocene auriferous gravels, western foothills of California's Sierra Nevada. In 1878, Lesquereux named this Aralia whitneyi in honor of a former California State Geologist. Image courtesy Lorraine Cazassa.

Two leaves from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Left to right: Matches closely what paleobotanist H. D. Macguinitie called Quercus distincta, an extinct species of evergreen Eocene oak similar to the living Coast live oak. Right--A specimen that matches what H. D. Macginitie called Phytocrene sordida, a species that most closely resembles a living Phytocrene evergreen vine now native to Myanmar, Sumatra, Java, and the Philippines; that distinctive reddish coloration to the Chalk Bluffs Flora specimen signifies that its original cuticle has been preserved intact--a genuine rarity in the fossil record. The cuticle is that thin layer on the upper epidermis of leaves that helps protect against mechanical injury, excessive water loss, and fungal attack. Photos courtesy the California Academy of Sciences from a publicly accessible site.

A leaf from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Quite similar to what paleobotanist H. D. Macguinitie called Acer aequidentatum, an extinct maple that shows characteristis of two living species--the Red maple and the trident maple (now native to China). Photo courtesy the California Academy of Sciences from a publicly accessible site.

A leaf from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Seems quite close in appearance to what paleobotanist H. D. Macguinitie called Persea pseudo-carolinensis, which is similar to the modern swampbay, an evergreen tree native to the southeastern United States.

A freshly dug leaf from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. It's one of several types of evergreen laurels that paleobotanist H. D. MacGinitie described from the Chalk Bluffs Flora in his classic work A Middle Eocene Flora From The Central Sierra Nevada, 1941, Carnegie Institute of Washington Publication 534.

Left and right: Leaves from the middle Eocene auriferous gravels, western foothills of California's Sierra Nevada. Left--A leaf from the extinct sycamore Macginitiea whitneyi, Chalk Bluff hydraulic gold mine It resembles the living sycamore Platanus lindeniana of east-central Mexico to Guatemala. Scale at lower left is in inches (top, beginning with blue bar at far left) and centimeters. Photograph courtesy the California Academy of Sciences (from a publicly accessible site). I edited and processed the image through photoshop.

Right--Two overlapping leaves from the Malakoff Diggins hydraulic gold mine. Collected by the late paleobotanists Howard Schorn and Jack A. Wolfe on August 14, 2003. Larger of the two leaves is closest to what paleobotanist H. D. MacGinitie called Hydrangeo californica--an extinct hydrangea (hortensia) that resembles the living Hydrangeo strigosa, native to China.

Smaller specimen at lower right agrees closely with what paleobotanist H. D. MacGinitie called Laurophyllum fremontensis, an extinct member of the evergreen laurel family that has no direct modern counterpart, though it does show close resemblances to three living genera: Cryptocarya--native to Andaman Is., Argentina Northeast, Assam, Bangladesh, Bismarck Archipelago, Borneo, Brazil North, Brazil Northeast, Brazil South, Brazil Southeast, Brazil West-Central, Cambodia, Cape Provinces, Chile Central, Chile South, China South-Central, China Southeast, Christmas I., Comoros, East Himalaya, Ecuador, Fiji, French Guiana, Hainan, Hawaii, India, Jawa, KwaZulu-Natal, Laos, Lesser Sunda Is., Madagascar, Malawi, Malaya, Maluku, Mozambique, Myanmar, Nansei-shoto, Nepal, New Caledonia, New Guinea, New South Wales, Nicobar Is., Niue, Norfolk Is., Northern Provinces, Northern Territory, Panamá, Peru, Philippines, Queensland, Samoa, Solomon Is., Sri Lanka, Sulawesi, Sumatera, Swaziland, Taiwan, Tanzania, Thailand, Tibet, Tonga, Uruguay, Vanuatu, Vietnam, Western Australia, Zambia, Zimbabwe; Machilus--endemic to Bangladesh, Cambodia, China South-Central, China Southeast, Hainan, India, Japan, Jawa, Kazan-retto, Korea, Laos, Lesser Sunda Is., Myanmar, Ogasawara-shoto, Sumatera, Taiwan, Vietnam; and Nectandra--now lives in Argentina Northeast, Argentina Northwest, Belize, Bolivia, Brazil North, Brazil Northeast, Brazil South, Brazil Southeast, Brazil West-Central, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Haiti, Honduras, Jamaica, Leeward Is., Mexico Central, Mexico Gulf, Mexico Northeast, Mexico Northwest, Mexico Southeast, Mexico Southwest, Nicaragua, Panamá, Paraguay, Peru, Puerto Rico, Suriname, Trinidad-Tobago, Uruguay, Venezuela, Windward Is.

A fossil magnolia leaf from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada, figured by paleobotanist H. D. MacGinitie in his classic work A Middle Eocene Flora From The Central Sierra Nevada, Carnegie Institute of Washington Publication 534, 1941. Called scientifically Magnolia dayana--an extinct magnolia that closely resembles the living umbrella magnolia, native to the Appalachian Mountains, the Ozarks, and the Ouachita Mountains of the eastern United States.

Fossil leaves from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada, figured by paleobotanist H. D. MacGinitie in his classic work A Middle Eocene Flora From The Central Sierra Nevada, 1941, Carnegie Institute of Washington Publication 534. Left--Platanus appendiculata, an extinct sycamore that is similar to the modern American sycamore, native to the eastern to central United States and northeastern Mexico. Right--Liquidamber californicum, an extinct liquidamber which resembles the living American sweetgum, native the southeastern United States, Mexico, and Central America.

Fossil leaves from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada, figured by paleobotanist H. D. MacGinitie in his classic work A Middle Eocene Flora From The Central Sierra Nevada, 1941, Carnegie Institute of Washington Publication 534. Left--Neolitsea lata, an extinct member of the laurel family, with evergreen leaves, that resemblances the modern Neolitsea chuii of southern China, a tree that grows to 60 feet. Right--Rhamnus calyptus, a presumed extinct buckthorn that is quite similar to the living Rhamnus nepalensis native to India, China, and Malaysia.

Two leaves from the middle Eocene auriferous gravels, Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada. Left to right: A specimen that in secondary venation, margins, and overall shape closely resembles what paleobotanist H. D. MacGinitie identified as Chaetoptelea pseudo-fulva, an extinct species that is similar to the living Mexican elm, endemic to Mexico and Central America.

Right--One of several species of evergreen laurels that H. D. MacGinitie described from the middle Eocene Chalk Bluffs Flora. A significant specimen. It's the first fossil leaf that provides unequivocal paleobotanical evidence that the middle Eocene auriferous gravels can be correlated stratigraphically with the leaf-bearing middle Eocene Ione Formation in the vicinity Ione, Amador County, California, roughly 62 miles southwest of the Chalk Bluff hydraulic gold mine. The leaf came from an horizon in the middle Eocene auriferous gravels that bears specimens that are not only identical to the leaves recovered from the Ione Formation (entire margins, with no serrations or lobes, for example), but are also preserved with the same distinctive reddish-brown iron-stained coloration; this is in obvious contrast to the fossil flora found in the auriferous gravels' chocolate shales, which produce numerous leaves with serrations and lobes--all invariably preserved as dark brown to black carbonized impressions (Chalk Bluffs Flora leaves with original cuticle are of course preserved in orange to reddish tones).

The implications of this discovery are far-reaching, indeed. For example, the middle Eocene Ione Flora (Ione Formation, in the general area of Ione, California (lower western foothills of the Sierra Nevada) accumulated in close proximity to sea level along the eastern shores of the Domengine-Ione Seaway, which had transgressed (flooded) the Tertiary Great Central Valley, while the Buckeye Flat middle Eocene plants lived at an altitude between 3,000 and 4,000 feet; thus, the sea level Ione leaves--all with entire (smooth) margins--can no longer be used as reliable indicators of a baseline sea level paleoenvironment, since identical botanical forms also occur in the higher-elevation Chalk Bluffs Flora of Buckeye Flat.

Paleobotanist H. D. MacGinitie actually began his monumental investigations of the Chalk Bluffs Flora at Buckeye Flat in 1933 before he re-discovered the stratigraphically correlative chocolate shale beds at the Chalk Bluff hydraulic gold mine.

A chunk of as-yet unidentified petrified wood from the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Petrified wood used to be abundant at the Chalk Bluff mine (and most of the other numerous 19th Century hydraulic operations in California's northern Mother Lode district), including fallen logs and quite sizable pieces that the old time hyraulickers stacked in great piles so that the Eocene permineralized botanic specimens would not interfere with gold extraction activities.

An archival photograph of folks sitting atop a petrified log from the middle Eocene auriferous gravels, exposed by hydraulickers in the mid 1800s at the Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Photograph taken sometime between 1933 and 1938. From the volume A Middle Eocene Flora From The Central Sierra Nevada, by H. D. MacGinitie, Carnegie Institute of Washington Publication 534, 1941.

Petrified wood (genus-species undetermined) weathers out of the middle Eocene auriferous gravels at the Buckeye Flat hyraulic gold mine, western foothills of California's Sierra Nevada; for scale perspective, that geology hammer is 13 inches long. Ppaleobotanist H. D. MacGinitie actually began his monumental investigations of the Chalk Bluffs Flora at Buckeye Flat in 1933 before he re-discovered the stratigraphically correlative chocolate shale beds at the Chalk Bluff hydraulic gold mine.

A petrified burl (genus-species undetermined) weathers out of the middle Eocene auriferous gravels at the Buckeye Flat hyraulic gold mine, western foothills of California's Sierra Nevada; for scale perspective, that geology hammer is 13 inches long. Paleobotanist H. D. MacGinitie actually began his monumental investigations of the Chalk Bluffs Flora at Buckeye Flat in 1933 before he re-discovered the stratigraphically correlative chocolate shale beds at the Chalk Bluff hydraulic gold mine.

Left to right--Petrified wood (genus-species undetermined) weathers out of the middle Eocene auriferous gravels at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada; for scale perspective, that geology hammer is 13 inches long.

Right--An archival photograph from the classic volume A Middle Eocene Flora From The Central Sierra Nevada, by H. D. MacGinitie, Carnegie Institute of Washington Publication 534, 1941. That's a stump from an extinct sycamore embedded in place in the middle Eocene auriferous gravels at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada; photograph taken between 1933 and 1938. Paleobotanist H. D. MacGinitie actually began his monumental investigations of the Chalk Bluffs Flora at Buckeye Flat in the early 1930s before he re-discovered the stratigraphically correlative chocolate shale beds at the Chalk Bluff hydraulic gold mine.

 

On-Site Images

A panoramic perspective, looking roughly northeast, across the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Hydraulickers worked everything here from the immediate foreground to the reddish-brown cliff at upper left to center, ultimately excavating downward approximately 400 feet through the auriferous gravels to the local metamorphic bedrock, where the fabulous "inner channel" (or "blue ground")--only tens of feet wide in most places--yielded vast fortunes in gold. The younger bench gravels, within which the leaf-bearing chocolate shales occur, yielded far inferior concentrations of the precious metal. Chalk Bluff ridge, proper, lies along the skyline; its composed of latest Eocene (about 34 million years old) rhyolite tuff.

A panoramic perspective, looking roughly northeast, across the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Hydraulickers worked everything here from the immediate foreground to the reddish-brown cliff at upper left to center, ultimately excavating downward approximately 400 feet through the auriferous gravels to the local metamorphic bedrock, where the fabulous "inner channel" (or "blue ground")--only tens of feet wide in most places--yielded vast fortunes in gold. The younger bench gravels, within which the leaf-bearing chocolate shales occur, yielded far inferior concentrations of the precious metal. Chalk Bluff ridge, proper, lies along the skyline; it's composed of latest Eocene (about 34 million years old) rhyolite tuff. Photograph courtesy the late paleobotanist Howard Schorn.

Along the main path through the Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Chalk Bluff ridge, proper, lies directly ahead; it's composed of latest Eocene-age (approximately 34 million years old) unfossiliferous rhyolite tuff.

Looking southward from the rim of the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Those 200 to 300 foot cliffs of middle Eocene auriferous gravels were created when mid 19th Century hydraulickers burrowed down to local metamorphic bedrock (at least 400 feet below the original surface of the land), in search of high grade gold concentrations.

Top and bottom: Two views looking northeast to roughly the same southern Chalk Bluff ridge section, western foothills of California's Sierra Nevada. Youngest acummulations of the middle Eocene aurifeous gravels comprise the slopes. Fossil leaves occur in lenticular clay lenses about halfway up the incline. Top photo snapped in latest 20th Century; bottom photograph taken between 1933 and 1938--from the volume A Middle Eocene Flora From The Central Sierra Nevada, by H. D. MacGinitie, Carnegie Institute of Washington Publication 534, 1941.

Left--An unexploited cliff face of middle Eocene auriferous gravels that the mid 19th Century hydraulickers left behind at the Chalk Bluff hydraulic gold mine, California. Note the progressive upward fining of the gold-bearing sedimentary material, culminating in a localized exposure of the leaf-bearing chocolate shales at the very top. Right--A "sneaky"-quasi-hidden exposure of leaf-bearing chocolate shales (marked with the green letters Chocolate Shales), interbedded with the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. For scale perspective, that geology hammer, just to the right of the green lettering, is 13 inches long.

Left--An encounter with an unexcavated bed of leaf-bearing chocolate shales (marked with the black letters at middle left--CS), interbedded with the middle Eocene auriferous gravels, Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Right--A closeup of the middle Eocene auriferous gravels at the Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada; white quartz pebbles and darker-colored metamorphic clasts set in a matrix of coarse sand comprise the gold-bearing gravels. That geology hammer is 13 inches long, by the way. Note clumps of Sierra lupine (Lupinus grayi) at base of the exposure; photograph taken in May.

Freshly excavated leaf-bearing chocolate shales at the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. Some 70 species of fossil plants--mostly similar to subtropical types that now grow in southern Mexico--have been described from the middle Eocene Chalk Bluffs Flora--that is, the total aggregate of specimens recovered from all localities in the chocolate shales exposed by hydraulic methods in the northern Sierra Nevada district during the mid to late 1800s. That geology hammer is 13 inches long, by the way.

Clumps of Sierra lupine (Lupinus grayi) observed at the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada; photograph taken in May.

Scotch Broom (Cytisus scoparius), a member of the Pea family, blooming at the great Chalk Bluff hydraulic gold mine, western foothills of California's Sierra Nevada. A plant native to southern Europe and northern Africa; photograph taken in May.

An undisturbed exposure of leaf-yielding chocolate shales (marked by the black letters--CS, at lower right) lies within the middle Eocene auriferous gravels at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada. Paleobotanist H. D. MacGinitie began his monumental scientific analysis of the Chalk Bluffs Flora here at Buckeye Flat in 1933, before he rediscovered the stratigraphically correlative and prolific chocolate shale beds at the Chalk Bluff hydraulic gold mine.

The late paleobotanist Howard Schorn (from 1964 to 1993, Collections Manager of Fossil Plants at the University California Museum of Paleontology) collects fossil leaves at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada, from a major quarrying excavation in chocolate shales that accumulated during middle Eocene times (about 48 to 45 million years ago) in a subtropical climate similar to today's southern Mexico along the vast floodplains of the Tertiary Yuba River, which dropped great quantities of gold. Photograph taken August 13, 2003. Paleobotanist H. D. MacGinitie began his monumental scientific analysis of the Chalk Bluffs Flora here at Buckeye Flat in 1933, before he rediscovered the stratigraphically correlative and prolific chocolate shale beds at the Chalk Bluff hydraulic gold mine.

The late paleobotanist Jack A. Wolfe (longtime member of the United States Geological Survey) collects fossil leaves at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada, from chocolate shales that accumulated during middle Eocene times (about 48 to 45 million years ago) in a subtropical climate similar to today's southern Mexico along the vast floodplains of the Tertiary Yuba River, which dropped great quantities of gold. Photograph taken August 13, 2003. Paleobotanist H. D. MacGinitie began his monumental scientific analysis of the Chalk Bluffs Flora here at Buckeye Flat in 1933, before he rediscovered the stratigraphically correlative and prolific chocolate shale beds at the Chalk Bluff hydraulic gold mine.

Left--The late paleobotanist Howard Schorn (from 1964 to 1993, Collections Manager of Fossil Plants at the University California Museum of Paleontology) assumes a classic paleobotanical position to collect fossil leaves at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada, from a major quarrying excavation in chocolate shales that accumulated during middle Eocene times (about 48 to 45 million years ago) in a subtropical climate similar to today's southern Mexico along the vast floodplains of the Tertiary Yuba River, which dropped great quantities of gold. Photograph taken August 13, 2003. Paleobotanist H. D. MacGinitie began his monumental scientific analysis of the Chalk Bluffs Flora here at Buckeye Flat in 1933, before he rediscovered the stratigraphically correlative and prolific chocolate shale beds at the Chalk Bluff hydraulic gold mine.

Right--The late paleobotanist Jack A. Wolfe (longtime member of the United States Geological Survey) collects fossil leaves at the Malakoff Diggins hydraulic gold mine, western foothills of California's Sierra Nevada. Photograph taken August 14, 2003.

Left--A major quarrying excavation in chocolate shales at the Buckeye Flat hydraulic gold mine, western foothills of California's Sierra Nevada; the leaf-bearing shales accumulated during middle Eocene times (about 48 to 45 million years ago) in a subtropical climate similar to today's southern Mexico along the vast floodplains of the Tertiary Yuba River, which dropped great quantities of gold. Paleobotanist H. D. MacGinitie began his monumental scientific analysis of the Chalk Bluffs Flora here at Buckeye Flat in 1933, before he rediscovered the stratigraphically correlative and prolific chocolate shale beds at the Chalk Bluff hydraulic gold mine.

Right--Cliffs of middle Eocene auriferous gravels left behind by mid 19th Century hydraulickers at the Malakoff Diggins hydraulic gold mine, western slopes of California's Sierra Nevada---but one of numerous such abandoned open pit gold-extraction localities in Northern California that operated from roughly 1855 to 1884.

Top and bottom--Middle Eocene auriferous gravels remain untouched at the Malakoff Diggins hydraulic gold mine, western foothills of California's Sierra Nevada--but one of numerous such abandoned open pit gold-extraction localities in Northern California that operated from roughly 1855 to 1884.

A pond develops at the base of a cliff of middle Eocene auriferous gravels left behind at the Dutch Flat hydraulic gold mine, western foothills of California's Sierra Nevada--but one of many abandoned open pit gold-extraction sites in Northern California that operated from roughly 1855 to 1884. Photograph courtesy Wayne Hsieh.

One of the most accessible, extensive exposures of unexploited middle Eocene auriferous gravels lies in this cut along the northern side of Interstate 80, about 1 mile east of the Gold Run Rest Stop. The roadcut runs for approximately a half mile, revealing in wonderful geologic detail the fossil thalwegs of the Tertiary Yuba River, which dropped great quantities of gold here. A Google Earth street car perspective that I edited and processed through photoshop.

The late paleobotanists Howard Schorn (at left--April 26, 1935-October 18, 2013) and Jack A. Wolfe (July 10, 1936-August 12, 2005) by a rented U-Haul van at the Northern Queen Inn, Nevada City, California, on August 18, 2003. Truck is filled with boxes of middle Eocene fossil leaves that Schorn, Wolfe, and geologist/geophysicist Clement G. Chase collected from many abandoned hydraulic gold mines, northern Sierra Nevada district, California. Howard Schorn is preparing here to transport that important collection back to the archival paleobotanical repository at the University California Museum of Paleontology in Berkeley.

Paleobotanist Howard Schorn delivers a fossil-filled U-Haul truck to the University California Museum of Paleontology, on campus at the University of California, Berkeley. The vehicle contains boxes of middle Eocene fossil leaves that Schorn, paleobotanist Jack A. Wolfe, and geologist/geophysicist Clement G. Chase collected from many abandoned hydraulic gold mines, northern Sierra Nevada, California, during a paleobotanical expedition in the summer of 2003. Photograph taken on August 18, 2003.

Paleobotanist Howard Schorn completes the transfer of boxes of middle Eocene leaves to the archival paleobotanical collections at the University California Museum of Paleontology in Berkeley. Howard Schorn, paleobotanist Jack A. Wolfe, and geologist/geophysicist Clement G. Chase collected the fossils from many abandoned hydraulic gold mines, northern Sierra Nevada, California, during a paleobotanical expedition in the summer of 2003. Photograph taken on August 18, 2003.

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Web sites I have created pertaining to fossils

  • Fossils In Death Valley National Park: A site dedicated to the paleontology, geology, and natural wonders of Death Valley National Park; lots of on-site photographs of scenic localities within the park; images of fossils specimens; links to many virtual field trips of fossil-bearing interest.
  • Fossil Insects And Vertebrates On The Mojave Desert, California: Journey to two world-famous fossil sites in the middle Miocene Barstow Formation: one locality yields upwards of 50 species of fully three-dimensional, silicified freshwater insects, arachnids, and crustaceans that can be dissolved free and intact from calcareous concretions; a second Barstow Formation district provides vertebrate paleontologists with one of the greatest concentrations of Miocene mammal fossils yet recovered from North America--it's the type locality for the Bartovian State of the Miocene Epoch, 15.9 to 12.5 million years ago, with which all geologically time-equivalent rocks in North American are compared.
  • A Visit To Fossil Valley, Great Basin Desert, Nevada: Take a virtual field trip to a Nevada locality that yields the most complete, diverse, fossil assemblage of terrestrial Miocene plants and animals known from North America--and perhaps the world, as well.
  • Fossils At Red Rock Canyon State Park, California: Visit wildly colorful Red Rock Canyon State Park on California's northern Mojave Desert, approximately 130 miles north of Los Angeles--scene of innumerable Hollywood film productions and commercials over the years--where the Middle to Late Miocene (13 to 7 million years old) Dove Spring Formation, along with a classic deposit of petrified woods, yields one of the great terrestrial, land-deposited Miocene vertebrate fossil faunas in all the western United States.
  • Late Pennsylvanian Fossils In Kansas: Travel to the midwestern plains to discover the classic late Pennsylvanian fossil wealth of Kansas--abundant, supremely well-preserved associations of such invertebrate animals as brachiopods, bryozoans, corals, echinoderms, fusulinids, mollusks (gastropods, pelecypods, cephalopods, scaphopods), and sponges; one of the great places on the planet to find fossils some 307 to 299 million years old.
  • Fossil Plants Of The Ione Basin, California: Head to Amador County in the western foothills of California's Sierra Nevada to explore the fossil leaf-bearing Middle Eocene Ione Formation of the Ione Basin. This is a completely undescribed fossil flora from a geologically fascinating district that produces not only paleobotanically invaluable suites of fossil leaves, but also world-renowned commercial deposits of silica sand, high-grade kaolinite clay and the extraordinarily rare Montan Wax-rich lignites (a type of low grade coal).
  • Ice Age Fossils At Santa Barbara, California--Journey to the famed So Cal coastal community of Santa Barbara (about a 100 miles north of Los Angeles) to explore one of the best marine Pleistocene invertebrate fossil-bearing areas on the west coast of the United States; that's where the middle Pleistocene Santa Barbara Formation yields nearly 400 species of pelecypod bivalve mollusks, gastropods, chitons, scaphopods, pteropods, brachiopods, bryozoans, corals, ostracods (minute bivalve crustaceans), worm tubes, and foraminifers.
  • Trilobites In The Marble Mountains, Mojave Desert, California: Take a trip to the place that first inspired my life-long fascination and interest in fossils--the classic trilobite quarry in the Lower Cambrian Latham Shale, in the Marble Mountains of California's Mojave Desert. It's a special place, now included in the rather recently established Trilobite Wilderness, where some 21 species of ancient plants and animals have been found--including trilobites, an echinoderm, a coelenterate, mollusks, blue-green algae and brachiopods.
  • Dinosaur-Age Fossil Leaves At Del Puerto Creek, California: Journey to the western edge of California's Great Central Valley to explore a classic fossil leaf locality in an upper Cretaceous section of the upper Cretaceous to Paleocene Moreno Formation; the plants you find there lived during the day of the dinosaur.
  • Early Cambrian Fossils Of Westgard Pass, California: Visit the Westgard Pass area, a world-renowned geologic wonderland several miles east of Big Pine, California, in the neighboring White-Inyo Mountains, to examine one of the best places in the world to find archaeocyathids--an enigmatic invertebrate animal that went extinct some 510 million years ago, never surviving past the early Cambrian; also present there in rocks over a half billion years old are locally common trilobites, plus annelid and arthropod trails, and early echinoderms.
  • A Visit To Ammonite Canyon, Nevada: Explore one of the best-exposed, most complete fossiliferous marine late Triassic through early Jurassic geologic sections in the world--a place where the important end-time Triassic mass extinction has been preserved in the paleontological record. Lots of key species of ammonites, brachiopods, corals, gastropods and pelecypods.
  • Fossils In Millard County, Utah: Take virtual field trips to two world-famous fossil localities in Millard County, Utah--Wheeler Amphitheater in the trilobite-bearing middle Cambrian Wheeler Shale; and Fossil Mountain in the brachiopod-ostracod-gastropod-echinoderm-trilobite rich lower Ordovician Pogonip Group.
  • Paleozoic Era Fossils At Mazourka Canyon, Inyo County, California: Visit a productive Paleozoic Era fossil-bearing area near Independence, California--along the east side of California's Owens Valley, with the great Sierra Nevada as a dramatic backdrop--a paleontologically fascinating place that yields a great assortment of invertebrate animals.
  • Late Triassic Ichthyosaur And Invertebrate Fossils In Nevada: Journey to two classic, world-famous fossil localities in the Upper Triassic Luning Formation of Nevada--Berlin-Ichthyosaur State Park and Coral Reef Canyon. At Berlin-Ichthyosaur, observe in-situ the remains of several gigantic ichthyosaur skeletons preserved in a fossil quarry; then head out into the hills, outside the state park, to find plentiful pelecypods, gastropods, brachiopods and ammonoids. At Coral Reef Canyon, find an amazing abundance of corals, sponges, brachiopods, echinoids (sea urchins), pelecypods, gastropods, belemnites and ammonoids.
  • Fossils From The Kettleman Hills, California: Visit one of California's premiere Pliocene-age (approximately 4.5 to 2.0 million years old) fossil localities--the Kettleman Hills, which lie along the western edge of California's Great Central Valley northwest of Bakersfield. This is where innumerable sand dollars, pectens, oysters, gastropods, "bulbous fish growths" and pelecypods occur in the Etchegoin, San Joaquin and Tulare Formations.
  • Field Trip To The Kettleman Hills Fossil District, California: Take a virtual field trip to a classic site on the western side of California's Great Central Valley, roughly 80 miles northwest of Bakersfield, where several Pliocene-age (roughly 4.5 to 2 million years old) geologic rock formations yield a wealth of diverse, abundant fossil material--sand dollars, scallop shells, oysters, gastropods and "bulbous fish growths" (fossil bony tumors--found nowhere else, save the Kettleman Hills), among many other paleontological remains.
  • A Visit To The Sharktooth Hill Bone Bed, Southern California: Travel to the dusty hills near Bakersfield, California, along the eastern side of the Great Central Valley in the western foothills of the Sierra Nevada, to explore the world-famous Sharktooth Hill Bone Bed, a Middle Miocene marine deposit some 16 to 15 million years old that yields over a hundred species of sharks, rays, bony fishes, and sea mammals from a geologic rock formation called the Round Mountain Silt Member of the Temblor Formation; this is the most prolific marine, vertebrate fossil-bearing Middle Miocene deposit in the world.
  • High Sierra Nevada Fossil Plants, Alpine County, California: Visit a remote fossil leaf and petrified wood locality in the Sierra Nevada, at an altitude over 8,600 feet, slightly above the local timberline, to find 7 million year-old specimens of cypress, Douglas-fir, White fir, evergreen live oak, and giant sequoia, among others.
  • In Search Of Fossils In The Tin Mountain Limestone, California: Journey to the Death Valley area of Inyo County, California, to explore the highly fossiliferous Lower Mississippian Tin Mountain Limestone; visit three localities that provide easy access to a roughly 358 million year-old calcium carbate accumulation that contains well preserved corals, brachiopods, bryozoans, crinoids, and ostracods--among other major groups of invertebrate animals.
  • Middle Triassic Ammonoids From Nevada: Travel to a world-famous fossil locality in the Great Basin Desert of Nevada, a specific place that yields some 41 species of ammonoids, in addition to five species of pelecypods and four varieties of belemnites from the Middle Triassic Prida Formation, which is roughly 235 million years old; many paleontologists consider this specific site the single best Middle Triassic, late Anisian Stage ammonoid locality in the world. All told, the Prida Formation yields 68 species of ammonoids spanning the entire Middle Triassic age, or roughly 241 to 227 million years ago.
  • Fossil Bones In The Coso Range, Inyo County, California: Visit the Coso Range Wilderness, west of Death Valley National Park at the southern end of California's Owens Valley, where vertebrate fossils some 4.8 to 3.0 million years old can be observed in the Pliocene-age Coso Formation: It's a paleontologically significant place that yields many species of mammals, including the remains of Equus simplicidens, the Hagerman Horse, named for its spectacular occurrences at Hagerman Fossil Beds National Monument in Idaho; Equus simplicidens is considered the earliest known member of the genus Equus, which includes the modern horse and all other equids.
  • Field Trip To A Vertebrate Fossil Locality In The Coso Range, California: Take a cyber-visit to the famous bone-bearing Pliocene Coso Formation, Coso Mountains, Inyo County, California; includes detailed text for the field trip, plus on-site images and photographs of vertebrate fossils.
  • Fossil Plants At Aldrich Hill, Western Nevada: Take a field trip to western Nevada, in the vicinity of Yerington, to famous Aldrich Hill, where one can collect some 35 species of ancient plants--leaves, seeds and twigs--from the Middle Miocene Aldirch Station Formation, roughly 12 to 13 million years old. Find the leaves of evergreen live oak, willow, and Catalina Ironwood (which today is restricted in its natural habitat solely to the Channel Islands off the coast of Southern California), among others, plus the seeds of many kinds of conifers, including spruce; expect to find the twigs of Giant Sequoias, too.
  • Fossils From Pleistocene Lake Manix, California: Explore the badlands of the Manix Lake Beds on California's Mojave Desert, an Upper Pleistocene deposit that produces abundant fossil remains from the silts and sands left behind by a great fresh water lake, roughly 350,000 to 19,000 years old--the Manix Beds yield many species of fresh water mollusks (gastropods and pelecypods), skeletal elements from fish (the Tui Mojave Chub and Three-Spine Stickleback), plus roughly 50 species of mammals and birds, many of which can also be found in the incredible, world-famous La Brea Tar Pits of Los Angeles.
  • Field Trip To Pleistocene Lake Manix, California: Go on a virtual field trip to the classic, fossiliferous badlands carved in the Upper Pleistocene Manix Formation, Mojave Desert, California. It's a special place that yields beaucoup fossil remains, including fresh water mollusks, fish (the Mojave Tui Chub), birds and mammals.
  • Trilobites In The Nopah Range, Inyo County, California: Travel to a locality well outside the boundaries of Death Valley National Park to collect trilobites in the Lower Cambrian Pyramid Shale Member of the Carrara Formation.
  • Ammonoids At Union Wash, California: Explore ammonoid-rich Union Wash near Lone Pine, California, in the shadows of Mount Whitney, the highest point in the contiguous United States. Union Wash is a ne plus ultra place to find Early Triassic ammonoids in California. The extinct cephalopods occur in abundance in the Lower Triassic Union Wash Formation, with the dramatic back-drop of the glacier-gouged Sierra Nevada skyline in view to the immediate west.
  • A Visit To The Fossil Beds At Union Wash, Inyo County California: A virtual field trip to the fabulous ammonoid accumulations in the Lower Triassic Union Wash Formation, Inyo County, California--situated in the shadows of Mount Whitney, the highest point in the contiguous United States.
  • Ordovician Fossils At The Great Beatty Mudmound, Nevada: Visit a classic 475-million-year-old fossil locality in the vicinity of Beatty, Nevada, only a few miles east of Death Valley National Park; here, the fossils occur in the Middle Ordovician Antelope Valley Limestone at a prominent Mudmound/Biohern. Lots of fossils can be found there, including silicified brachiopods, trilobites, nautiloids, echinoderms, bryozoans, ostracodes and conodonts.
  • Paleobotanical Field Trip To The Sailor Flat Hydraulic Gold Mine, California: Journey on a day of paleobotanical discovery with the FarWest Science Foundation to the western foothills of the Sierra Nevada--to famous Sailor Flat, an abandoned hydraulic gold mine of the mid to late 1800s, where members of the foundation collect fossil leaves from the "chocolate" shales of the Middle Eocene auriferous gravels; all significant specimens go to the archival paleobotanical collections at the University California Museum Of Paleontology in Berkeley.
  • Early Cambrian Fossils In Western Nevada: Explore a 518-million-year-old fossil locality several miles north of Death Valley National Park, in Esmeralda County, Nevada, where the Lower Cambrian Harkless Formation yields the largest single assemblage of Early Cambrian trilobites yet described from a specific fossil locality in North America; the locality also yields archeocyathids (an extinct sponge), plus salterella (the "ice-cream cone fossil"--an extinct conical animal placed into its own unique phylum, called Agmata), brachiopods and invertebrate tracks and trails.
  • Fossil Leaves And Seeds In West-Central Nevada: Take a field trip to the Middlegate Hills area in west-central Nevada. It's a place where the Middle Miocene Middlegate Formation provides paleobotany enthusiasts with some 64 species of fossil plant remains, including the leaves of evergreen live oak, tanbark oak, bigleaf maple, and paper birch--plus the twigs of giant sequoias and the winged seeds from a spruce.
  • Ordovician Fossils In The Toquima Range, Nevada: Explore the Toquima Range in central Nevada--a locality that yields abundant graptolites in the Lower to Middle Ordovician Vinini Formation, plus a diverse fauna of brachiopods, sponges, bryozoans, echinoderms and ostracodes from the Middle Ordovician Antelope Valley Limestone.
  • Fossil Plants In The Dead Camel Range, Nevada: Visit a remote site in the vicinity of Fallon, Nevada, where the Middle Miocene Desert Peak Formation provides paleobotany enthusiasts with 22 species of nicely preserved leaves from a variety of deciduous trees and evergreen live oaks, in addition to samaras (winged seeds), needles and twigs from several types of conifers.
  • Early Triassic Ammonoid Fossils In Nevada: Visit the two remote localities in Nevada that yield abundant, well-preserved ammonoids in the Lower Triassic Thaynes Formation, some 240 million years old--one of the sites just happens to be the single finest Early Triassic ammonoid locality in North America.
  • Fossil Plants At Buffalo Canyon, Nevada: Explore the wilds of west-central Nevada, a number of miles from Fallon, where the Middle Miocene Buffalo Canyon Formation yields to seekers of paleontology some 54 species of deciduous and coniferous varieties of 15-million-year-old leaves, seeds and twigs from such varieties as spruce, fir, pine, ash, maple, zelkova, willow and evergreen live oak
  • High Inyo Mountains Fossils, California: Take a ride to the crest of the High Inyo Mountains to find abundant ammonoids and pelecypods--plus, some shark teeth and terrestrial plants in the Upper Mississippian Chainman Shale, roughly 325 million years old.
  • Field Trip To The Copper Basin Fossil Flora, Nevada: Visit a remote region in Nevada, where the Late Eocene Dead Horse Tuff provides seekers of paleobotany with some 42 species of ancient plants, roughly 39 to 40 million years old, including the leaves of alder, tanbark oak, Oregon grape and sassafras.
  • Fossil Plants And Insects At Bull Run, Nevada: Head into the deep backcountry of Nevada to collect fossils from the famous Late Eocene Chicken Creek Formation, which yields, in addition to abundant fossil fly larvae, a paleobotanically wonderful association of winged seeds and fascicles (bundles of needles) from many species of conifers, including fir, pine, spruce, larch, hemlock and cypress. The plants are some 37 million old and represent an essentially pure montane conifer forest, one of the very few such fossil occurrences in the Tertiary Period of the United States.
  • A Visit To The Early Cambrian Waucoba Spring Geologic Section, California: Journey to the northwestern sector of Death Valley National Park to explore the classic, world-famous Waucoba Spring Early Cambrian geologic section, first described by the pioneering paleontologist C.D. Walcott in the late 1800s; surprisingly well preserved 540-510 million-year-old remains of trilobites, invertebrate tracks and trails, Girvanella algal oncolites and archeocyathids (an extinct variety of sponge) can be observed in situ.
  • Petrified Wood From The Shinarump Conglomerate: An image of a chunk of petrified wood I collected from the Upper Triassic Shinarump Conglomerate, outside of Dinosaur National Monument, Colorado.
  • Fossil Giant Sequoia Foliage From Nevada: Images of the youngest fossil foliage from a giant sequoia ever discovered in the geologic record--the specimen is Lower Pliocene in geologic age, around 5 million years old.
  • Some Favorite Fossil Brachiopods Of Mine: Images of several fossil brachiopods I have collected over the years from Paleozoic, Mesozoic and Cenozoic-age rocks.
  • In Search Of Vanished Ages--Field Trips To Fossil Localities In California, Nevada, And Utah--My fossils-related field trips in full print book form (pdf). 98,703 words (equivalent to a medium-size hard cover work of non-fiction); 250 printed pages (equivalent to about 380 pages in hard cover book form); 27 chapters; 30 individual field trips to places of paleontological interest; 60 photographs--representative on-site images and pictures of fossils from each locality visited.

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