56 GLACIAL AND SUEFACE GEOLOGY OF THE PACIFIC COAST. 



a careful survey and an accurate map. Traces of former glaciation were 

 observed in abundance on the eastern slope, nearly down to Silver Mountain 

 City, 6,516 feet above the sea-level. Just below that raining settlement 

 volcanic rocks cover the surface, and no more striation was noticed. It is 

 probable, however, that the glacier descended considerably lower on this 

 side, for numerous blocks of granite were seen perched high up on the sides 

 of the lava-covered ridges, where they must have been left by ice. 



The western slope of the Sierra, from Carson Pass nearly to Donner Pass, 

 or the crossing of the Central Pacific Railroad, a distance of about fifty miles, 

 is drained by the numerous branches of the American River. For a consid- 

 erable portion of this distance the summit of the Sierra is divided into two 

 nearly parallel ranges of about equal height, and between them lies by far 

 the largest and most important mountain lake of California, Lake Tahoe, 

 which is about twenty-one miles long, and from nine to twelve in breadth. 

 The elevation of the range on the west side of this lake, in its highest point, 

 a little exceeds 9,000 feet. Pyramid Peak, ten miles southwest of the south 

 end of Lake Tahoe, and just north of the Placerville road to Carscm Valley, 

 which ascends the South Fork of the American, is the highest point north 

 of Silver Mountain until we reach Lassen's Peak, having an elevation of 

 about 10,100 feet, which is nearly 500 feet less than the last-named summit. 

 The other prominent points along the range at the head of the American 

 River are nearly a thousand feet lower than Pyramid Peak.* Mount Stanford, 

 just north of Donner Pass, is 9,102 feet in elevation. Of the passes along 

 the range between this point and Pyramid Peak the highest is that of Squaw 

 Valley, crossed by a trail only, and 8,774 feet in elevation ; the pass trav- 

 ersed by the Central Pacific Railroad is only 7,017 feet above the sea-level. 



The point farthest soutli in the American -River basin where traces of 

 former glaciation have been noticed by the Geological Survey is at Silver 

 Lake, near Carson Pass, at the head of Alpine Creek, one of the branches of 

 the South Fork of the American. In fact, the region all about the Carson 

 Pass, which has nearly the same elevation as the Silver Mountain Pass, 

 exhibits abundant proofs of the former presence of glaciers. Near Tragedy 

 Springs boulders of granite were seen resting on the lava tables, as if left 

 there by ice, although the striation was wanting. 



Farther north, all about Hope Valley, and around a small lake in Luther's 

 Pass, which connects with the Johnston Pass, are abundant glacial traces. 



* Sec Table of Daronietrif Altitiules, in Appt'iulix to the gravel volume. 



