No. 381.] A HALF-CENTURY OF EVOLUTION. 661 
“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 peneplain and carried it to 
its present condition.” 
Le Conte ! states that the Sierra Nevada was upheaved at the 
end of the Jurassic period. This corresponded to the Appa- 
lachian revolution, which occurred at the end of the Paleozoic 
era. 
But during the long ages of the Cretaceous 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 fea- 
tures of an old topography, with its gently flowing curves. ... At the end 
of the Tertiary came the great lava streams running down the river chan- 
nels and displacing the rivers ; the heaving 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 con- 
sequent down-cutting of these to form the present deep canyons and the 
resulting wild, almost savage, scenery of these mountains. 
This view is further carried out by J. S. Diller, from his 
Studies of the northern part of the Sierra Nevada, including 
the borders of the Sacramento Valley and the Klamath Moun- 
tains. He shows that northern California, during the earlier 
portion of the auriferous gravel period, was by long-continued 
degradation worn down to base-level conditions. ‘The moun- 
tain ranges,” he says, “were low, and the scenery was every- 
where characterized by gently flowing slopes. s 
“ The topographic revolution consisted in the development 
out of such conditions of the conspicuous mountain ranges of 
to-day. 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 face 
of that portion of the range.” 2 
According to Lindgren, the Sierra Nevada was eroded to, or 
almost to, a peneplain during Cretaceous times, and the moun- 
1 Bull. Geol. Soc. Amer., vol. ii, pp. 327, 328 
2 Fourteenth Ann. Rep. U. S. Geol. Survey, Pt. ii, p. 433. 
