This mortar and pestle were found by J.H. Neale in tertiary deposits dating 33-55 million years old. 
 
On August 2, 1890, J.H. Neale signed the following statement about his discoveries:  "In 1877 Mr. J.H. Neale was superintendent of the Montezuma tunnel Company, and ran the Montezuma tunnel into the gravel underlying the lava of Table Mountain, Tuolumne County....At a distance of between 1400 and 1500 feet from the mouth of the tunnel, or of between 200 and 300 feet beyond the edge of the solid lava, Mr. Neale saw several spear-heads, of some dark rock and nearly one foot in length.  On exploring further, he himself found a small mortar three or four inches in diameter and of irregular shape.  This was discovered within a foot or two of the spear-heads.  He then found a large well-formed pestle....
 
"...Mr. Neale declares that it is utterly impossible that these relics can have reached the position in which they were found excepting at the time the gravel was deposited, and before the lava cap formed.  There was not the slightest trace of any disturbance of the mass or of any natural fissure into it by which access could have been obtained either there or in the neighborhood."