THE TOPOGRAPHY OF CALIFORNIA 567 
that if these canyons were filled level to the tops of the ridges 
the result would be an irregular, slightly warped, tilted plain. 
In general the grade of this tilted plain is quite regular from 
the low elevation of the California Valley to the top of the moun- 
tains. This western slope was probably once a region worn 
down almost to base level or to a peneplain. By the uplift of 
the mountains a great fault was developed along the eastern face 
and the whole Sierra crust-block tilted to the westward. The 
streams quickened by the uplift again set to work on the pene- 
plain and carved it to its present condition. According to Pro- 
fessor Joseph Le Conte :* 
The Sierra was formed, as we now know, by lateral crushing and strata- 
folding at the end of the Jurassic. But during the long ages of the Creta- 
ceous and Tertiary this range was cut down to very moderate height. .... 
The rivers by long work had finally reached their base-levels and rested. 
The scenery had assumed all the features of an old topography, with its 
gently flowing curves. .... At the end of the Tertiary came the great lava 
streams running down the river channels and displacing the rivers ; the heav- 
ing up of the Sierra crust-block on its eastern side, forming the great fault- 
cliff there and transferring the crest to the extreme eastern margin; the 
great increase of the western slope and the consequent rejuvenescence of the 
vital energy of the rivers; the consequent down-cutting of these to form the 
present deep canyons and the resulting wild, almost savage, scenery of these 
mountains. 
J. S. Diller’s researches in the northern part of the Sierra 
Nevada further strengthen these theories, as the following quo- 
tations from him will show: 
A study of the ancient topographic features upon the borders of the 
Sacramento valley, in the Klamath Mountains, and upon the western slope of 
the Sierra Nevada, shows that during the earlier portion of the auriferous 
gravel period northern California, by long-continued degradation, was finally 
reduced approximately to base-level conditions. The mountain ranges were 
low, and the scenery was everywhere characterized by gently flowing slopes. 
.... The topographic revolution consisted in the development out of such 
conditions of the conspicuous mountain ranges of today. The northern end 
of the Sierra Nevada has since been raised at least 4000 feet, and possibly as 
much as 7000 feet, and a fault of over 3000 feet developed along the eastern 
* Bull. Geol. Soc. Am., Vol. II, pp. 327-328. 
