292 =I. C. Russell—Subaérial Deposits of North America. 
In the United States it occurs from near the sea-level in Arizona, 
and even below sea-level in Southern California, up to an elevation 
of at least six or eight thousand feet, along the eastern border of 
the Rocky Mountains, and in the elevated valleys of New Mexico, 
Colorado and Wyoming. It occupies depressions of all sizes up to 
valleys having an area of hundreds of square miles. Although 
occurring throughout the Arid Region, it can be studied to best 
advantage in the drainless and lakeless basins at Nevada, Utah, and 
Arizona. 
Thickness— The maximum thickness of the adobe is always 
difficult to determine, for the reason that it is still accumulating, and 
has not been sufficiently dissected by erosion to expose sections of 
any considerable depth. That it not infrequently has a depth of 
many hundreds of feet is apparent to one who traverses the valley 
in which it oceurs. The profiles of very many of these valleys 
indicate that they have probably been filled to a depth of at least 
two or three thousand feet. In the larger valleys there are rocky 
crests, called “lost mountains,” which project above the broad level 
desert surface, and are in reality the summits of precipitous mountains 
that have been almost completely buried beneath recent accumula- 
tions. These qualitative observations are supported by a few 
quantitative measurements. 
At Sandy, about six miles south of Salt Lake City, Utah, and at 
a distance of two or three miles west of the west base of the 
Wasatch Mountains, a well was bored a few years since, in search 
of artesian water, which penetrated fine yellow earth with occasional 
layers of sand, gravel and clay, to a depth of about 1500 feet, with- 
out reaching the rock-bottom of the basin. The material taken 
from near the bottom of this well was of the same character as that 
occurring at the surface over a large number of valleys throughout 
the Arid Region. 
The boring at Sandy is in the basin of Lake Bonneville (Quater- 
nary), but the entire depth of material penetrated cannot be referred 
to the deposits of that lake. Older lakes, in which sands and clays 
must have been accumulated, probably existed in the same basin in 
pre-Bonneville times, and the depression must also have been filled 
by purely subaérial deposits. It is impossible to determine whether 
the comminuted material brought up from the well was deposited 
under water or not, but the precise manner in which its accumula- 
tion took place does not concern us so much at present as the 
evidence which the well affords of the great depth of superficial 
material occurring in Great Salt Lake Valley, and, it is to be pre- 
sumed, in adjacent valleys as well. 
A second well over 1300 feet deep was bored a few years since 
near Humboldt Lake, Neyv., which penetrated material of the same 
general character as that brought up from the well near Salt Lake 
City, and, as in the former instance, did not reach the true rock- 
bottom of the basin in which it was bored. This well was located 
in a valley once occupied by the waters of Lake Lahontan (Quater- 
nary), but only the extreme upper portion of the material penetrated 
can be referred to the sediment of that lake. 
