Plate 2.—Regional description. This text stays at a general level, describing the 
region as a whole. These broad generalizations are later amplified. 
The Colorado Plateau is a region of high plateaus, cut by- 
deep canyons, and studded by isolated mountains. It is lo 
cated in the "four corners" area of Arizona, New Mexico, 
Colorado and Utah (see Fig. 1.1) and covers some 130,000 sq. 
mi. It is a dry, sparsely settled region where lack of water 
precludes large scale agriculture and settlement, but its 
wealth of natural resources is bringing rapid development. 
RELIEF - The region is underlain by nearly horizontal beds 
of sandstone, shale and limestone, which form elevated plat 
eaus. Many isolated areas have been uplifted forming high 
mountains, which have either retained their sedimentary cov 
ering or have weathered until basaltic laccoliths remain. 
The upper sedimentary strata of the plateaus are resistant 
to erosion and their surfaces have a mature drainage system 
of winding draws and shallow lakes. V.here these strata have 
been worn through erosion has accelerated creating canyons. 
These exposed faces are more vulnerable to weathering so 
canyon walls and fault scarps are crumbling and retreating. 
There has been considerable volcanic acivity In the region 
and many bf the. Jilateaus have high volcanic mountains tower 
ing above them, and the surrounding area is covered by cin 
der cones, lava flows and volcanic necks. 
DRAINAGE - The region is drained by the Colorado River and 
its tributaries. The swift current of the Colorado carries 
a heavy load of silt which keeps its channel cutting ever 
deeper. The main tributaries, the Little Colorado, the San 
Juan, and the Green Rivers flow inward into a wide basin in 
the center of the region and then join the Colorado just be 
fore it enters the Grand Canyon. Perennial streams are rare. 
CLIMATE - The region has a semi-aria climate, which is ex 
tremely variable and_ strongly influenced by elevation. Elev 
ation creates climatff- zones, with a subarctic climate on the 
higher mountains, which rise above 12,000 ft., a temperate 
climate on the high plateaus from 8,000 to 7,000 ft., and a 
semi-desert climate below 7,000 ft. The mountains receive 
large amounts of precipitation, ranging up to 40" annually, 
which is about equally divided between summer rains and win 
ter snows. The high plateaus receivea20" - 30" annually, 
and lower elevations receive between 5" and 20". Droughts 
of long duration are common. High summer temperatures in 
the low elevations cause strong updrafts, creating local 
convectional storms. The storms generally form over the 
higher elevations then drift over other areas. This gives 
the higher elevations almost daily rains during the summer, 
but the lowlands have a progressively smaller chance of 
getting the benefit of these drifting storms the farther 
they are from the high country. There are strong winds in 
spring which disturb the formation of updrafts, and as a 
result there is a period of drought through June each year. 
COLORADO PLATEAD 
SOILS - The soils of the region are generally thin, poorly 
developed residual clays and sandy clays resulting froa the 
wasting of sedimentary rock. Due to the light rainfall 
many of the soils at lower elevations are alkaline, produc 
ing little more than alkali tolerant shrubs. Slow soil 
movement before the disturbance of vegetation filled many 
basins with deep, fertile deposits of soil, but since the 
advent of white men and their herds heavy grazing has reduc 
ed the vegetation cover and many of these deposits are now 
cut by deep gullies. Other basin soils have been irrigated 
and are extremely productive. Most of the volcanic areas 
are so recent that soils have not yet formed, except where 
fine cinders and ash fell. This material acts as a mulch 
and makes agriculture possible in some unirrigated places. 
NATURAL VEGETATION - The mountains and high plateaus of the 
region have a zone of heavy coniferous forests. The forests 
are composed of spruce and fir on the mountain tops, with 
open stands of pine covering the high plateaus. At lower 
elevations there is a zone of open savanna composed of low 
pinon, Juniper and grasslands. Open rangelands of sparse 
weeds and shrubs cover many low plateaus and basins, with 
barren lands at the lowest elevations. 
RURAL CULTURE - Livestock raising is one of the principal 
occupations and Isolated ranches are found throughout the 
region. Large numbers of cattle and sheep are grazed on the 
high plateaus and mountains in summer and on the low plat 
eaus and basins in winter. Many marks of this activity are 
visible, such as earth tanks, windmills, corrals and fences. 
Indian reservations occupy large areas and have very primi 
tive settlements. Some are pueblos of adobe houses, while 
other areas have scattered circular huts called "hogans". 
Many people are engaged in timber cutting and sawmilling or 
in fuel wood and post cutting. Oil and gas production, and 
more recently the processing of uranium, is rapidly expanding. 
Small settlements are often found around these processing 
plants, but more often settlements are supported by a com 
bination of activities and are located at transport Junctions. 
URBAN CULTURE - Large settlements have sprung up near irrig 
ation and road and rail junctions, which has placed most 
of them in the low basins where these occur. These settle 
ments are laid out in a characteristic gridiron pattern, 
oriented to the railroad, with large blocxs and wide streets, 
without shade trees. 
TRANSPORTATION - There are only four rail lines in the region 
and they follow routes through the lower basins where they are 
paralleled by paved highways. An open net of other paved roads 
branches off from these axes, and large areas are served by low 
standard dirt roads. Rut roads and trails serve the mountains. 
REPORT OF COMMISSION VII GVII-85