Finds from mine shafts can be dated more securely than those from hydraulic mines and surface deposits of gravel.  Many shafts were sunk at Table Mountain in Tuolumne County.  Whitney and others reported that miners found stone tools and human bones there, in the gold-bearing gravels sealed beneath thick layers of a volcanic material called latite. 

Discoveries from the auriferous gravels just above the bedrock are probably 33.2 to 55 million years old.  The more important discoveries from Table Mountain add up to a considerable weight of evidence.  J.D. Whitney personally examined a collection belonging to Dr. Snell, consisting of stone spoons, handles, spearheads, and a human jaw - all found in the auriferous gravels beneath the latite cap of Tuolumne Table Mountain.  Whitney remarked that all the human fossils uncovered in the gold-mining region, including this one, were of the anatomically modern type.

Writing 11 years before the discovery of the Java ape-man, Pithecanthropus erectus, Whitney concluded that, "Man, thus far, is nothing but man, whether found in Pliocene, Post-pliocene, or recent formations."