| A fossil plant from the Carson Pass area, Sierra Nevada, California. It's a petrified stump preserved in an unnamed geologic rock unit dated by radiometric methods (radioactive isotope analyses) at 14.7 million years old; the material from which the stump protrudes is a trachyandesite ash flow tuff, with subordinate debris flow deposits. Photograph courtesy geologists Cathy J. Busby and Keith Putirka. |