ORIGINAL STREAMS IN GENERAL DESERT-LEVELING 269 
the influences of a desiccating climate and as vast volumes of 
mountain waste deeply filled their valleys to form the present level 
intermont plains. As these arroyos are looked upon today they 
are the last vestiges of a once extensive consequent drainage. 
In this connection one other point should be briefly noted. 
The general plains-surface of the region under consideration lies 
about a mile above sea-level; and above this surface rise another 
mile the rugged and isolated desert ranges. As in the case of the 
Great Basin region, it was long the custom to regard the mountain- 
ranges as tilted and upraised blocks, deeply dissected on all sides 
from which the resulting waste was carried directly out into the 
intermont basins. According to this view, the arid climate came 
over the region while it was already a mountainous country, much 
as it is today except more deeply sculptured, like the Rockies or 
the Appalachians are now. 
There is another hypothesis applicable to the origin of these 
streams of the desert ranges; one which more closely accords with 
the conditions imposed by an arid climate. It is postulated that 
the mountains are products of differential erosion on an elevated 
plain composed of alternating hard and soft rock-belts.' The 
erosion of more than 5,000 feet is ascribed to deflation with little 
or no aid from stream-action.?, That wind-scour under favorable 
conditions is amply competent to accomplish such work, that it 
is as potent an erosive agent as stream-corrasion and the washings 
of the rain in a moist climate is fully shown by the recent writings of 
many observers in various parts of the world, although in this 
country this subject has not as yet received the attention that it 
merits. Of these, mention may be made of the work of Obruchew? 
in central Siberia, of Walther? in North Africa, of La Touche’ 
in the western Rajputana in India, of Berg® and Ivchenko’ in the 
t Journal of Geology, XVII (1909), 31. 
2 Bull. Geol. Soc. America, XXI (1910), 592. 
3 Verh. Imp. min. Gesellsch. St. Petersburg, (2), XX XIII (1895), 260. 
4 Das Gesetz d. Wiistenbildung im Gegenwart u. Vorseit, 1900. 
5 Mem. Geol. Sur. India, XX XV (1902), Io. 
6 Pédologie pour 1902, p. 37. 
7 Ann. géol. min. Russie, VII (1904), Pt. I, 43. 
