Description:
The principal ore deposits of Arizona are in the southern, central,
and western portions of the state, which physiographically
are part of the Basin and Range province, southwest of the Colorado
Plateau (PI. I).
The Basin and Range province is characterized by numerous
subparallel mountain ranges separated by plains or valleys. Most
of these ranges trend northwest to north, parallel to the margin
of the Colorado Plateau; but in southeastern Arizona, southern
New Mexico, and northeastern Sonora, they trend northward,
transverse to the edge of the Plateau. The mountains rise
abruptly from plains or valleys, the margins of which in many
places are pediments cut on hard rock. Some of the plains form
closed basins (bolsons, playas), but most of them are drained.
The Basin and Range province in Arizona is divisible into the
Mountain Region and the Desert Region- (PIs. I and II). The
Mountain Region forms a belt 60 to 100 miles wide that contains
most of the large ore deposits. Its longest range measures about
55 miles, the widest 20 miles, and the highest peak more than
10,000 feet above sea level or 7,000 feet above adjacent valleys or
plains. Broad plain-forming valleys are exceptional, but several
with maximum widths of 20 to more than 30 miles appear in the
southeastern portion. 136 p.