An ichnofossil (trace fossil), called scientifically Ophiomorpha, from the Ione Formation, western foothills of the Sierra Nevada. It is the fossilized burrow of a species of shrimp-like animal, most likely a callianassid shrimp. Here is a comprehensive description of just what Ophiomorpha represents from the web page at http://www.envs.emory.edu/ichnology/Ophiomorpha.htm:
"Ophiomorpha is a branching burrow with either horizontal, oblique, or vertical box-like networks; the burrow exterior is characterized by a knobby texture formed by a pelletal lining, but in some cases only an internal mold of the burrow is evident. Ophiomorpha is interpreted as a combined dwelling and feeding burrow made by a shrimp-like animal; modern callianassid shrimp show the same burrow geometry and pelletal reinforcement of their burrows."
The roughly 45 million-year-old specimen came from an extraordinarily rich locality on private property in Amador County--a specific site currently under formal paleobotanical study by Dr. Jack A. Wolfe (retired member of the United States Geological Survey) and Howard E. Schorn (retired Collections Manager of Fossil Plants at the University California Museum of Paleontology in Berkeley), among others, who hope to use the fossils to help approximate the paleoelevation of the ancestral Sierra Nevada region during the geologic past.
Please note: All fossil localities in the Ione Formation of Amador County, California, presently occur on private property; explicit permission from the land owners must be secured before collecting fossils there.