FRAMEWORK OF ARIZONA 
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FRAMEWORK OF ARIZONA GEOLOGY 
By Charles Keyes 
Few are the spots of earth that present such a wealth of geologic 
phenomena as does the southwestern United States. Greater vari¬ 
ety of features and structures manifest themselves crowded togeth¬ 
er in small spaces than perhaps anywhere else on the face of our 
globe. Almost every known kind of geologic process appears to 
find expression in some way or other. Every known cause of geo¬ 
graphic products seems to have been in operation. Everything geol¬ 
ogical is on such gigantic scale that it has to be viewed from afar, 
from distances measured in miles and scores of miles, in order to 
get proper perspective of relations. 
Essentially a country especially distinguished for its mountains, 
the dominant physiographic feature of Arizona is really the plain. 
It is above this general plains-surface that the mountains tower. 
Noteworthy is the fact that this vast plain is far along in its evo¬ 
lution towards the foundations below which land-depletion can 
no longer go. It is not the normal peneplain controlled in its 
downward course by the waters of the ocean, but the base-level 
of eolic erosion which is quite independent of the sea. 
The physiography of Arizona is broadly divisible into three prin¬ 
cipal tracts: (1) the High Plateau, or Colorado Dome, of the 
northeast; (2) the Bolson Lowlands of the southwest; and (3) 
a broad Dissected Hill-land Belt between stretching out diagonally 
across the state from southeast to northwest. The present moun¬ 
tains are mainly the hard, tilled strata from which the associated 
soft deposits are largely removed all around through subaerial ero¬ 
sion. Volcanic piles everywhere stud the surface. 
As physiographic features, streams are inconsequential in this 
land of little rain; and the chief watercourse, the Rio Colorado, a 
