GENERAL GEOGRAPHY. ' 13 
The mountain ranges throughout western Arizona, with a few not- 
able exceptions, lie in general parallel to the border of the plateau. 
In general, also, the mountains become smaller and more completely 
isolated away from the plateau. In central Arizona, where the dis- 
tinction between mountain and plain is most marked, rugged moun- 
tains extend from Mogallon Mesa to the Superstition Mountains, a 
distance of 70 miles, where they give place gradually through such 
isolated groups as the Phoenix Mountains, Estrella Mountains, etc., 
to the still smaller hills of southwestern Arizona. As the mountains 
become less prominent the valleys broaden and finally blend into a 
plain completely surrounding the isolated mountain groups. The 
topographic character of northwestern Arizona lies between these ex- 
tremes, « the area being about equally divided between mountain and 
plain. 
Mountains. — The mountains of northwestern Arizona occur in four 
more or less distinct groups. The first consists of a series of cliffs at 
the eastern border of the region known as the Grand Wash, Cotton- 
wood, Aquarius, and Yampai cliffs. The first three form a practi- 
cally continuous escarpment, extending from Colorado River south- 
ward to Williams Canyon, a distance of about 125 miles. The Grand 
Wash Cliffs, extending from Colorado River to Music Mountain, a dis- 
tance of about 50 miles, is composed of crystalline rock at the base, 
overlain by the sedimentary formations of the plateau region. At 
Music Mountain this escarpment divides, the lower or crystalline part 
continuing southward under the names of the Cottonwood and Aqua- 
rius cliffs and forming the edge of the Truxton Plateau, while the upper 
or sedimentary part recedes to the east, under the name of the Yampai 
Cliffs. With the lower group of cliffs may be included the Aquarius 
and Artillery mountains, which form the southward extension of the 
Aquarius Cliffs. 
A second group, consisting of the White Hills, Cerbat, and Hualpai 
mountains and the Aubrey Hills, forms a broken range parallel to 
the cliffs at the west. The White Hills and the Aubrey Hills are in- 
conspicuous as topographic features, but the two central sections are 
prominent. The Hualpai Mountains attain a maximum altitude of 
8,266 feet in Hualpai Peak, and the Cerbat Mountains an altitude of 
somewhat more than 7,000 feet in Cherums Peak. 
A third group, lying still farther to the west, is commonly known 
as the Black Mountain Range, and consists of the Black Mountains 
proper, Black Mesa, and the Mohave Mountains. This range is rela- 
tively low, except at its northern end, but is continuous from Colo- 
rado River southward to Sacramento Wash, where it is broken down 
for a few miles before attaining prominence again in the Mohave 
Mountains. . 
