Above. Drawing of the controversial Calaveras Skull.
Whatever you want to call it, the tertiary period was a long, long time ago. The oldest remains of what is considered "modern" humans are from an Israeli cave and dated to about 400,000 years ago which is about 2.4 million years after the end of the tertiary period.
The famed tertiary rivers extended from South America to the Klondike and deposited rich gold deposits wherever they flowed. The dead rivers are the source of virtually all of the placer gold in the Mother Lode so they have been well studied by geologists and miners.
The dead rivers of the tertiary are widely accepted by geologists to be at least 2.8 million years old. Certainly they existed before the Sierra volcanic period which buried these rivers under hundreds of feet of lava and ash. There shouldn't be any human remains in the gravels because no humans existed 2.8 million years ago.
The Calaveras Skull is an outlier. It defies all scientific theory on the age of the gravels, or the age of humans. The find is well documented and was investigated shortly after its discovery by Dr. J.D. Whitney who was a California State Geologist responsible for mapping the tertiary gravels. Dr. whitney wrote on the discovery of the skull as follows:
"The manner in which the skull in question came into the writer's (Dr. Whitney) possession is as follows: June 18, 1866, Dr. William Jones of Murphy's, Calaveras County, a physician of extensive practice in that part of the mining region...wrote to the office of the Geological Survey of San Francisco, stating he had in his possession 'a human skull of Indian type, in a good state of preservation...which was recently found by Mr. Mattison and Co., in their claim on Bald Mountain, near Altaville and Angels, one hundred and thirty feet below the surface, and below the lava, in the cement and in close proximity to a completely petrified oak.
"Mr. Mattison, on being questioned, stated he took the skull from his shaft in February, 1866, with some pieces of wood found near it, and supposing it might be something of interest, carried it in a bag to the office of Wells, Fargo & Co.'s Express, at Angel's, and gave it to Mr. Scribner, the agent. He stated, the skull, was so embedded and encrusted with earthy and stony material that he did not recognize what it was.
"When delivered into the writer's hands its base was embedded in a conglomerate mass of ferruginous earth, water worn pebbles of much altered volcanic rock, calcareous tufa, and fragments of bones. This mixed material covered the whole base of the skull. A thin calcareous incrustation appears to have covered the whole skull when found.
"Nothing was done to the skull to alter its condition in any way, after it came into the writer's hands, until it had been examined by Dr. Wyman, when we together carefully chiseled off the foreign matter adhering to its base, as to expose the natural surface.
"In cutting away the mixed tufa and gravel which covered the face and base, several fragments of human bones were removed...These bones and fragments of bone might have belonged to the same individual to whom the skull had appertained; but, besides these, there was a portion of a human tibia of too small size to be referred to the same person. There were also some fragments of the bones of a small mammal.
"The skull, being as nearly deprived of its organic matter as fossil bones found in the tertiary usually are, and having had a large portion of its phosphate replace by carbonate of lime, is undoubtedly a fossil...Chemical analysis proves that it was not taken from the surface, but that it was dug up from somewhere, from some place where it had been long deposited, and where it had undergone those chmical changes which, so far as known, do not take place in objects buried near the surface."
The below table provides the results of Dr. Whitney's analsis:
Above. Chart showing chemical analysis of the Calaveras Skull.
Most people claim the skull was an elaborate hoax, if so it was truly well done by a bunch of miners. The most popular counter to the authenticity involves a story of several miners finding an Indian grave and deciding to play a joke on the local physician, they staged the finding of the skull and took it to the physician with several miners swearing to the authenticity of the find 130 feet underground. The physician then transferred it to Dr. Whitney.
If the hoax story is true it doesn't explain the chemical composition of the skull. For comparison the water content of opal, which is fossilized wood, is less than 3%. From the chart above one can see the skull has virtually no water content indicating it is very old indeed.
The second part of the argument agains the authenticity states it was a modern Indian skull which was then packed with tertiary material to present the appearance of age. This argument is refuted by the measurements taken by Dr. Whitney of the skull which are shown below:
Above. Measurements of the skull taken by Dr. Whitney, comparing to Native American skulls.
If Whitney's analysis is correct, and he was one of the few who physically examined the skull, then the discovery of the Calaveras Skull has the potential to turn what we know of history upside down.
It's doubtful modern man existed in the tertiary period which leads to only one other conclusion: the geologists are wrong. The tertiary gravels can't be 2.8 million years old. This theory is actually held by quite a few miners who have worked in, and around the tertiary gravels. Most miners who've spent any amount of time in the gravels can report finding fossilized mammal bones. During the time the underground placer mines were running it was actually quite common to find prehistoric mammal bones in the tertiary gravels deep underground.
At the Hornitos Mine, and in No.1 Gulch, five miles north of Hornitos, California, stone implements have been found in the gravels. In 1864 a large number of grinding stones were found. Accompanying the stones were other stone tools and the bones of mastadons indicating humans and mastadons existed at the same time in California.
Near Princeton, California, in 1863, a large number of stone artifacts were found embedded in the gravels including spearheads made from obsidian and large stone mortars and pestles. One of the mortars weighed over 50 pounds.
Near Sonora, in the limestone crevices, large numbers of mastodon bones were found by miners alongside large quantities of stone tools.
"It may be stated, in general, that all about Sonora the auriferous gravels which have been worked as placer mines, and the material filling the crevices in the limestone belt, have in great number of localities been found to be filled with the bones of animals of extinct species; and that with these many relics of the works of human hands have also been discovered, at various depths down to about a hundred feet."
Another human skull was found in the drift mines under Table Mountain in 1857. This skull was donated to the Boston Museum of Natural History. This skull was not nearly as intact as the Calaveras Skull and was found 180 feet below the surface and below the lava cap.
Whether the Calaveras Skull is real or not it is undisputed a large number of ancient bones, trees and human implements have been found within the gravels. How they got there remains disputed. Either these animals and humans lived alongside the tertiary rivers some 2.8 million years ago, or the tertiary rivers can't be as old as geologists believe.