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.

Please Note: All fossil sites are off-limits without permission from the landowners.