568 NOAH FIELDS DRAKE 
face of that portion of the range... . . The amount of uplift decreases rap- 
idly towards the Sacramento valley.” 
Mr. Waldemar Lindgren thinks the Sierra Nevada was eroded 
to, or almost to, a peneplain during Cretaceous times, and that 
the mountains elevated ina later Cretaceous period were worn 
down during Tertiary times merely to a gentle topography.” 
Of the origin of the range he says: 
At this time’... . the first break took place, separating the Sierra 
Nevada from the interior basin. The orogenic disturbance was probably of 
a twofold character. It included the tilting up of the whole region between 
the Wasatch and the Pacific in arching form, and a simultaneous breaking in 
and settling down of the higher portions of the arch. Thus the Sierra 
Nevada crust fragment was formed, the larger part of which has ever since 
remained a comparatively rigid block. Along the eastern margin the sys- 
tem of fractures was outlined which toward the close of the Tertiary was to 
be still further emphasized. 
The evidences that the Sierra Nevada is a tilted and eroded 
peneplain with a fault line along its eastern edge may be summed 
up as follows: 
(1) The present features of the western slope of the moun- 
tains resemble a tilted and dissected peneplain. The precipitous 
slope on the eastern side marks the fault line. 
(2) Fossil plants, which indicate a low altitude at the time 
of the deposition, have been found in the auriferous gravels in 
the northern part of the Sierra Nevada. 
(3) The auriferous gravels now found in the old river beds 
along the western slope of the Sierra Nevada must have been 
deposited in streams flowing down gentle grades. 
(4) Many of the old river valleys are terraced, showing suc- 
cessive stages of elevation as well as low stream grades.5 
(5) The present rivers flow directly across the upturned edges 
14th Ann. Rept. U.S. Geol. Surv., Part II, p. 433. 
2Jour. GEOL., Vol. IV, pp. 882, 894, 897, and 808. 
3JouR. GEOL., Vol. IV, p. 894. 
4J.S. DILLER, 14th Ann. Rept. U. S. Geol. Surv., pp. 421-422. 
5J. S. DILLER, 8th Ann. Rept. U. S. Geol. Surv., Part I, p. 429. 
