H. W. Turner — Glacial Pot-holes in California. 453 



Akt. LIX. — Glacial Pot-holes in California; by H. W. 

 Turner, of the United States Geological Survey. 



In the canon of the North Fork of the Mokelumne River, 

 California, about thirty miles a little west of south from Lake 

 Tahoe, and at an elevation above sea level of about 4,500 feet, 

 is a group of pot-holes in the granite. The canon here was 

 formerly the bed of a glacier, as is evidenced by the polish and 

 grooving of the rock and the perched bowlders. The rock 

 about is quite devoid of soil. The pot-holes are from two to 

 four feet in diameter and some of them are four feet deep. 

 The shape of some of them is nearly conical, others more 

 nearly cylindrical. Most of the pot-holes are eroded vertically, 

 but some of them are inclined. A number are quite shallow, 

 but even these are broad and saucer-shaped. The granite 

 flakes off in shells nearly parallel to its surface, and this would 

 account for the broad form of the pot-holes at the commence- 

 ment of their formation. 



The pot-holes are about 250 in number and from six inches 

 to six feet apart. They seldom or never coalesce and the 

 regularity of their arrangement is noticeable. The interior of 

 all of the holes is well rounded and smooth, as pot-holes usually 

 are. In some of them are rounded fragments of rocks ; others 

 are filled with sand and gravel. They cover a gently inclined 

 surface of about two thousand square feet. To the north is a 

 glaciated bank of granite, and the pot-holes occupy about the 

 position that would be expected if formed by water falling 

 over this bank. The height of the bank above the pot-holes 

 is approximately forty feet. One pot-hole exists in the side of 

 this bank several feet above its base. 



The river at the present time runs at a level of perhaps 

 twenty or thirty feet below the lowest pot-holes. The place 

 is locally known as Ham's Salt Springs. Salt water oozes out 

 from crevices in the rock and collects in several of the lower 

 pot-holes. By evaporation, salt (NaCl) crystallizes out so that 

 the water is usually covered with a thick layer of very pretty 

 hopper-shaped crystals. 



The Indians are said to have formerly congregated here, 

 attracted no doubt by the salt springs. Numerous small 

 arrow-heads, chiefly of jasper and obsidian, were found by my 

 party a little west of the pot-holes. At a point on the bare, 

 granite below the pot-holes and very near the river are several 

 small mortar holes such as are used by the Indians to grind up 

 acorns, and which are frequently found in bare rocks in the 

 Sierra Nevada. 



