The most notorious fossil discovered in the Gold Rush mines of California was the Calaveras skull.  In February 1866, Mr. Mattison, the principal owner of the mine on Bald Hill, near Angels Creek, removed this fossilized skull from a layer of gravel 130 feet below the surface.  The gravel was near the bedrock, underneath several distinct layers of volcanic material.  It was examined by J.D. Whitney, State Geologist of California, who presented a report on the Calaveras skull to the California Academy of Sciences on July 16, 1866, affirming that it was found in Pliocene strata.  This discovery caused a huge sensation in America and many believed it was a hoax.