It extends along the north side of the Stanilaus, which is a small river flowing in a south-westerly course through the county. The mountain is in the form of a ridge about two thousand feet above the present level of the river. At one point the river breaks through this ridge, which has been worn away for a considerable distance. From this point the ridge appears as a continuous mountain, stretching away to the south for a distance of twenty miles, from where it crosses the river. “As seen from a distance the Table Mountain reveals its origin at once, in the contrast between the long, straight line of its upper edge and the broken and curving ones which the eroded hills of the auriferous strata everywhere exhibit. Its dark color and comparative absence of trees and shrubs on its top and sides also indicate very clearly that the materials of which it is composed are very different from that of the surrounding hills.”4
This is the celebrated Table Mountain of Tuolumne County. It is simply a vast flow of lava. It must have been a grand sight when this river of fire came rolling down from its volcanic fount. Its present position on top of an elevated ridge is a very singular one. In explanation of that we arrive at some very important conclusions, and we can not fail to be impressed with the fact that countless ages have rolled away since that lava flood poured down the mountain side. “No one can deny that a stream of melted lava, running for forty miles down the slope of the Sierra, must have sought and found a depression or valley in which to flow; for it is impossible that it should have maintained for any distance its position on the crest of a ridge.” Lava is about as thick as molten iron, and would as surely seek some valley in which to flow as would so much water. “The valley of the Stanilaus, now two thousand feet deep, could not then have existed; for this flow of lava is clearly seen to have crossed it at one point.”
“The whole face of the country must, therefore, have undergone an entire change since the eruption took place, during which this mass of lava was poured out. The valley of the Stanilaus must have then been occupied by a range of mountains. The same is true of the other side, where now is the valley of Wood’s Creek; for such ranges must have existed in order to form and wall in the valley in which the current of lava flowed. There has been, therefore, an amount of denudation during the period since this volcanic mass took its position of not less than three or four thousand feet of perpendicular depth, and this surprising series of changes is not peculiar to one locality, but the whole slope of the Sierras, through the gold region, is the scene of similar volcanic outflows and subsequent remodeling of the surface into a new series of reliefs and depressions.”5
In order to fully realize the change here spoken of, an imaginary section of Table Mountains is here presented. Here we see the two valleys on the sides, and the mass of lava covering the top of the mountain. The dotted lines represent the position of the old line of hills, which must once have inclosed the valley down which coursed the fiery torrent.
We require to dwell on this, fact before we can fully understand its meaning. The “eternal hills,” two and three thousand feet in height, have been completely washed away, and where they stood is now a deep valley. But the old valley, protected by its stony covering, is now a mountain ridge; and this, we are told, is not a solitary instance, but the entire surface of the country has been thus denuded. We stand in awe before the stupendous results, which nature, working through vast cycles of time, has accomplished.
But if this lava flow took place in a pre-existing valley, we ought to find under the rocky covering beds of gravel, rolled stones, and other débris peculiar to a river bed. Such, in fact, we do find extended along directly underneath the lava, about fifteen hundred feet above the general level of the country. These old river gravels are found to be very rich in gold, and miners have tunneled into them in numerous places in search of the valuable metal. In order to determine the geological age of these gravels, and subsequent lava flow, a careful examination of portions of plants and bones of animals found therein has been made. The plants are pronounced by competent authority6 to be Pliocene, totally distinct from any specimens now growing in California. The animal remains are rhinoceroses, camels, and an extinct species of horse. The age of these gravels is, therefore, pronounced to be Pliocene. We would say in this connection that the auriferous gravels of California have been the object of a very careful research by Prof. Whitney. He adds to his conclusions that of another of the State geologists. We need not give in detail his arguments, but he reaches the conclusion that the auriferous gravels of the Pacific slope represent the whole of the Tertiary Age.7
We have seen that in the ancient gravels of European rivers archæologists have found the materials wherewith to build a fascinating story of man’s appearance in Quaternary times. We have underneath the lava flow of California the gravel beds of rivers far antedating the gravels of the Somme. It is therefore not a little interesting to learn from Prof. Whitney that he finds many proofs of the existence of man in the gravels of the Pliocene Age in California. Under the solid basalt of Table Mountain have been found many works of men’s hands, as well as the celebrated “Calaveras Skull.”