What is "calaveras skull"

Calaveras skull \Ca`la*ve"ras skull\ A human skull reported, by Prof. J. D. Whitney, as found in 1886 in a Tertiary auriferous gravel deposit, lying below a bed of black lava, in Calaveras County, California. It is regarded as very doubtful whether the skull really belonged to the deposit in which it was found. If it did, it indicates an unprecedented antiquity for human beings of an advanced type.

The Calaveras Skull was a human skull found by miners in Calaveras County, California, which was purported to prove that humans, mastodons, and elephants had coexisted in California. It was later revealed to be a hoax. Coincidentally, "calaveras" is the Spanish word for "skulls".