The majority of gold-bearing gravels were laid down in stream channels during the Eocene and Early Oligocene. During the Oligocene, Miocene, and Pliocene, volcanic activity in the same region covered some of the auriferous gravels with deposits of rhyolite, andesite, and latite. 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.
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 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. From the modern geological dating of the Table Mountain strata, it is apparent that the Calaveras skull was over 9 million years old. In their book Forbidden Archeology (1993) Michael Cremo and Richard Thompson documented numerous other cases showing that human beings like ourselves have existed on this planet for tens of millions, even hundreds of millions of years. See also: Whitney, J. D. (1880): The auriferous gravels of the Sierra Nevada of California. Harvard University, Museum of Comparative Zoology Memoir 6 (1); Cremo, M. (2003): The Nineteenth Century California Gold Mine Discoveries: Archeology, Darwinism, and Evidence for Extreme Human Antiquity. - World Archaeological Congress 5, June 21-26, 2003 Washington, D.C.; Cremo, M. (2014): Forbidden Archeology. - Talks at Google [63 m].