50 RECONNAISSANCE OF PART OF WESTERN ARIZONA. 
The floor of the Hualpai Valley is nearly level at an altitude of 
about 3,000 feet and is met on either side by mountain slopes at high 
angles. The plateau to the east drains away from Hualpai Valley 
into Colorado River, and the drainage from the White Hills and the 
Cerbat Mountains to the west and from the Hualpai and Peacock 
mountains to the south is so small as to be negligible. The only 
stream worthy of note that enters this great valley is Truxton Creek, 
the bed of which is usually dry, but which occasionally contains floods 
of great volume. 
Structure. — The Hualpai Valley is a structural trough formed by 
faulting and block tilting. The Grand Wash fault, with a displace- 
ment of 10,000 feet or more at the mouth of Grand Canyon, continues 
southward into the valley, together with several smaller faults to the 
west. The general trend of this fault zone in the vicinity of Colorado 
River, where it is best known, suggests that it may extend through 
the Hualpai Valley beneath the detrital accumulations and reappear 
in the fault west of the Hualpai Mountains. On the other hand, 
extensive displacements by faulting have taken place along the Cot- 
tonwood and Aquarius cliffs (see pp. 19-20), and it is possible that 
these cliffs mark th o -southward extension of the Grand Wash fault. 
At the northern *mk\ of the valley the sedimentary formations are 
tilted steeply to the east; along the eastern flank of the White Hills 
and Cerbat Mountains the sheets of basalt dip eastward beneath the 
valley floor. The trough formed by this downthrow to the east has 
been filled with rock debris to some unknown depth; a well bored 
700 feet deep near the head of Hualpai Wash did not pass through 
it. The material on the alluvial slopes is coarse, but in the center of 
the valley it is fine and is continually shifted by the winds. 
BIG SANDY VALLEY. 
Location and character. — The Big Sandy Valley is located between 
the Aquarius Cliffs on the east and the Hualpai Mountains and 
Aubrey Hills on th§ west, and extends from Hackberry southward 
to Williams River. The lowest part of the valley, known as Big 
Sandy Wash, lies at the foot of the cliffs as far south as Signal, but 
at this point the Big Sandy leaves the main valley and passes through 
Signal Canyon. Several streams of considerable size emerge from 
the plateau to the east through deep, narrow canyons and discharge 
into the Big Sandy. The largest of these are White Cliff, Trout, and 
Sycamore creeks. 
That portion of the valley between the Hualpai Mountains and 
Big Sandy Wash consists of a long, graded detrital slope (see fig. 2, 
p. 24), more or less deeply cut by parallel washes, such as Deluge 
Wash. This highly inclined detrital slope, the western fault scarp 
of the Hualpai Mountains, and the fault scarp to the east (Aquarius 
Cliffs) all terminate at the south in practically the same latitude. 
The southern end of the valley, between the Artillery Mountains and 
