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5.5.8 The Pierce Mortar

In 1870, Llewellyn Pierce gave the following written testimony (Whitney 1880, p. 266): “This is to certify that I, the undersigned, have this day given to Mr. C. D. Voy, to be preserved in his collection of ancient stone relics, a certain stone mortar, which has evidently been made by human hands, which was dug up by me, about the year 1862, under Table Mountain, in gravel, at a depth of about

200 feet from the surface, under the basalt, which was over sixty feet deep, and about 1,800 feet in from the mouth of the tunnel. Found in the claim known as the Boston Tunnel Company.” Whitney (1880, p. 266) said the mortar was 31.5 inches in circumference. Voy visited the site and saw the approximate place where the object was found (Whitney 1880, p. 267).

William J. Sinclair interviewed Llewellyn Pierce in 1902, a good 40 years after the original discovery was made. Sinclair (1908, p. 116) wrote: “The mortar from the Boston claim was [according to Pierce] as large as a sixteen-gallon milk bucket and would weigh about seventy-five pounds. It was found in hard gravel under the cement, and was taken out by Mr. Pierce while he was sitting on a candle box, breasting [sic] out gravel. . . . The mortar preserved in Voy’s collection is an oval boulder of hornblende andesite into which a hole has been worked, about four and three-quarters inches in greatest width, and three and three-quarters inches deep, dimensions to which those of a sixteen-gallon bucket must be regarded as a rather liberal approximation.” This last sarcastic remark appears calculated to cast doubt on Pierce’s testimony. But it should be recalled that the entire mortar was 31.5 inches in circumference, which is close to the size of the mouth of a tall sixteen gallon milk bucket commonly used in dairies.

Sinclair (1908, p. 117) added: “The deep gravels in the bottom of the Table Mountain channels, tapped by the Boston Tunnel and other workings, are largely inaccessible, but so far as known are not volcanic. The incongruity of associating an andesitic mortar . . . with the old prevolcanic gravels is at once apparent. The andesitic sands and gravels of Table Mountain lie above the auriferous gravel channels in which these relics were supposed to occur.” If Sinclair is correct that the mortar was found in the prevolcanic gravel, then it would be 33–55 million years old (Table 5.3, p. 371).

But what was the source of the andesite from which the Pierce mortar was made? The prevolcanic auriferous gravels contained boulders of different kinds of rock formed in previous ages, so who can say that there were no isolated andesite boulders in the ancient river channels? Furthermore, there may have been deposits of andesite as old as the prevolcanic gravels in other nearby areas of the Sierra Nevada mountains, and therefore andesite boulders or finished andesite mortars could have been transported by human agency to the region of Tuolumne Table Mountain.

In fact, Durrell (1966, pp. 187–189) reported four nearby sites, all north of Tuolumne Table Mountain, which are just as old as the prevolcanic auriferous gravels and contain deposits of hornblende andesite. These are the Wheatland Formation, at 100 miles; the Reeds Creek Formation, at 100 miles; Oroville Table Mountain, at 140 miles; and the Lovejoy Formation, at 200 miles.

Good portable andesite mortars might have been a valuable trade item, and might have been transported good distances by rafts or boats, or even by foot. In a study of California Indians, R. F. Heizer and M. A. Whipple reported the presence of basalt mortars in Marin County, north of San Francisco. The mortars ranged in weight from 20 to 125 pounds. Heizer and Whipple (1951, p. 298) stated: “Each of these pieces must have been carried to the spot from not less than 25 miles away, no mean task for the slightly built, barefoot Indians. Stone is completely lacking in the alluvial deposits of the valley floodplain of the Sacramento