FORMER GLACIATIOX AT THE HEAD OF THE AMERICAN. 57 



Around Pyramid Peak extensive ice-flows have existed in former times. 

 The rock of this lofty peak is all granite, which about the summit covers the 

 surface in large angular blocks. On the east side is a valley with much bare 

 rock, which is polished by glaciers, and contains several small lakes. The 

 large ice-flow which formed on this slope descended to the south, and passed 

 over a high precipice into the cailon of the American River, a short distance 

 above Slippery Ford. The name of the latter locality is suggestive of the 

 glacier-polished surface of the rock at the crossing of the stream. 



From Pyramid Peak the range extends in a nearly northerly direction for 

 about twelve miles, and in the gorges between the spurs leading down 

 from it to Lake Talioe glaciers formerly descended, probably nearly or 

 quite to the level of that fine sheet of water, which is about 6,250 feet in 

 altitude. There is also a high and somewhat isolated point, called Crystal 

 Peak, five miles north-northeast of Pyramid Peak and at the head of Fallen 

 Leaf Lake, which also sent down its glaciers to the east and north. In this 

 part of the range, which runs straight north from Pyramid Peak, a large 

 branch of the Middle Fork of the American River heads, running northwest 

 and joining the main stream at Big Meadows. This branch is called the 

 Rubicon, and its valley is polished and striated throughout its whole length. 

 The Little Rubicon, a much smaller stream, running nearly parallel with the 

 last-mentioned, exhibits similar features. According to Mr. Bowman, who 

 made a detailed survey of this region I'or the California Water Company, the 

 lowest point at which he observed glacial gravel in the course of his work 

 around the region drained by the Middle Fork of the American was a little 

 below Forney's, or Pilot Creek, at an altitude of about 5,000 feet above the 

 sea-level. 



From Burton Pass the main divide of the Sierra trends a little more to 

 the west of north, and is quite distinctly mai'ked as far north as Mount 

 Stanford, although declining gradually in elevation. The Twin Peaks and 

 Granite Chief are two prominent points in this division of the range ; the 

 former has an elevation of 8,724, the latter of 9,144 feet above the sea. Some 

 of the higher portions of the ridge are cap[)ed with tables of lava, irregularly 

 eroded away, as is so common an occurrence everywhere in the range from 

 the Sonora Pass northward. Glaciers, no doubt, made their wa}- down Ijoth 

 .sides of this portion of the range. Quite an extensive one must have 

 descended in the valley of the North Fork; but the upper portion of this 

 stream has been very little examined by the Survey. 



