THE TOPOGRAPHY OF CALIFORNIA 569 
of Mesozoic and Paleozoic beds on the lower slopes of the 
mountains. 
(6) The Tertiary lavas on the western slope of the Sierras 
cover a gentle topography." 
It has been noted that the Sierra Nevada is now deeply 
carved by the streams flowing down its western slope. The 
canyons vary in depth from a few hundred to six thousand feet ; 
their walls are very steep, and in places perpendicular; in the 
Yosemite and King’s River canyons there are perpendicular walls 
over three thousand feet high.? These canyons run approxi- 
mately at right angles to the trend of the mountains and parallel 
with each other. This direction and parallelism is especially 
true of the larger canyons, which form a series quite regularly 
spaced throughout the length of the mountains. 
The parallelism of the canyons is due principally to the two 
causes of uniform direction of tilting and the parallel system of 
fault and fissure lines. It is generally conceded that the great 
canyons, as well as many smaller ones, run along fault lines. 
And it has been observed*+ that often the canyon following 
one system of fissures crosses over to another system and fol- 
lows it. G. F. Becker has pointed out that in places these 
fissure lines are so close together as to amount to shattered 
zones, and that the main fissure systems cross at right angles.‘ 
So a probable explanation for such places as King’s River 
and Yosemite Valleys is that they are the locations of shattered 
zones removed by erosion, so that the fissures bounding the 
shattered zone now form the faces of the perpendicular exposed 
valley or canyon walls. 
It may be seen from the accompanying plate that the can- 
yons west of Lake Tahoe, especially North Yuba River, Middle 
WALDEMAR LINDGREN, JOUR. GEOL., Vol. IV, p. 897. 
2J. D. WHITNEY, Geol. Surv. Calif., Vol. I, pp. 410 and 421. JOHN MuIR, Cen- 
tury Magazine, Vol. XVIII, p. 488, and Vol. XXI, p. 80. 
3G. F. BECKER, Bull. Geol. Soc. Am., Vol. II, p. 68. The Rocks of the Sierra 
Nevada, by H. W. TuRNER, 14th Ann. Rept. U. S. Geol. Surv., p. 443. 
4G. F. BECKER, Bull. Geol. Soc. Am., Vol. II, p. 68. 
5 Bull. Geol. Soc. Am., Vol. II, pp. 50-51 and 68. 
