1915] SMILEY—LAKE TAHOE REGION 269 
nent peaks are Mt. Tallac (9785 feet), Rubicon Peak (9193 feet), 
Twin Peak (8924 feet), Tinker Knob (9020 feet), and Castle Peak 
(9139 feet). The average height of the ridge is above 8000 feet. 
To the west it falls by a gradual slope to valleys draining into the 
Yuba, American, and Cosumnes rivers. Its eastern side forms 
an abrupt scarp closely skirting Lake Tahoe and the valley of the 
Truckee River. From the lake this scarp appears in places to be 
almost sheer. From the summit of Mt. Tallac there is a descent 
Fic. 2,—Canadian zone: the high summit is Pyramid Peak 
of over 3000 feet in less than two miles. There is some reason to 
think that fairly uniform elevation of the ridge really represents 
the remnant of an ancient plateau, traces of which still persist on 
the south side of Mt. Tallac and Angora Peak. It has been sug- 
gested (1) that the summits themselves represent a still older 
erosion surface, but for this there is little direct evidence. This 
summit accordance is a general feature of the Sierra, particularly 
marked in the High Sierra (3). On this ancient upland lie the high 
alpine valleys, of which Faith, Hope, and Charity valleys south of 
Lake Tahoe are typical. 
The Carson Range, of which Freel’s Peak is the highest sum- 
mit, is less rugged than the Divide. Its summits are rounded or 
