Source : Webster's Revised Unabridged Dictionary (1913)

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.