The Cliff Ruins of Canyon de Chelly, Arizona | Page 5

it. This is the more common form, although isolated
mesas, bits of tableland completely engirdled by cliffs, are but little less
common.
The courses of the margins of the mesas are not regular. The cliffs
sometimes maintain an average trend through great distances, but in
detail their courses are extremely crooked; they wind in and out,
forming alternate alcoves and promontories in the wall, and frequently
they are cut through by valleys, which may be either narrow canyons or
interspaces 10 or even 20 miles wide.

The whole region has been subjected to many displacements, both
flexures of the monoclinal type and faults. Some of these flexures attain
a length of over 80 miles and a displacement of 3,000 feet, and the
faults reach even a greater magnitude. There is also an abundance of
volcanic rocks and extinct volcanoes, and while the principal eruptions
have occurred about the borders of the region, extending but slightly
into it, traces of lesser disturbances can be found throughout the
country. It has been said that if a geologist should actually make the
circuit of the plateau country, he could so conduct his route that for
three-fourths of the time he would be treading upon volcanic materials
and could pitch his camp upon them every night. The oldest eruptions
do not go back of Tertiary time, while some are so recent as probably to
come within the historic period--within three or four centuries.
The strata of the plateau country are remarkable for their homogeneity,
when considered with reference to their horizontal extensions; hardly
less so for their diversity when considered in their vertical relation.
Although the groups differ radically from each other, still each
preserves its characteristics with singularly slight degrees of variation
from place to place. Hence we have a certain amount of similarity and
monotony in the landscape which is aided rather than diminished by the
vegetation; for the vegetation, like the human occupants of this country,
has come under its overpowering influence. The characteristic
landscape consists of a wide expanse of featureless plains, bounded by
far-off cliffs in gorgeous colors; in the foreground a soil of bright
yellow or ashy gray; over all the most brilliant sunlight, while the
distant features are softened by a blue haze.
The most conspicuous formation of the whole region is a massive
bright-red sandstone out of which have been carved "the most striking
and typical features of those marvelous plateau landscapes which will
be subjects of wonder and delight to all coming generations of men.
The most superb canyons of the neighboring region, the Canyon de
Chelly and the Del Muerto, the lofty pinnacles and towers of the San
Juan country, the finest walls in the great upper chasms of the Colorado,
are the vertical edges of this red sandstone."

Of the climate of the plateau country it has been said that in the large
valleys it is "temperate in winter and insufferable in summer; higher up
the summers are temperate and the winters barely sufferable." It is as
though there were two distinct regions covering the same area, for there
are marked differences throughout, except in topographic configuration,
between the lowlands and the uplands or high plateaus. The lowlands
present an appearance which is barren and desolate in the extreme,
although the soil is fertile and under irrigation yields good crops.
Vegetation is limited to a scanty growth of grass during a small part of
the year, with small areas here and there scantily covered by the prickly
greasewood and at intervals by clumps of sagebrush; but even these
prefer a higher level, and develop better on the neighboring mesas than
in the valleys proper. The arborescent growth consists of sparsely
distributed cottonwoods and willows, closely confined to the river
bottoms. On intermediate higher levels junipers and cedars appear,
often standing so closely together as to seriously impede travel, but
they are confined to the tops of mesas and other high ground, the
valleys being generally clear or covered with sagebrush. Still higher up
yellow pines become abundant and in places spread out into
magnificent forests, while in some mountain regions scrub oak,
quaking asp, and even spruce trees are abundant.
In the mountain regions there is often a reasonable amount of moisture,
and some crops, potatoes for example, are grown there without
irrigation; but the season is short. In the Tunicha mountains the Navaho
raise corn at an altitude of nearly 8,000 feet, but they often lose the
crop from drought or from frost. On the intermediate levels and in the
lowlands cultivation by modern methods is practically impossible
without irrigation, except in a few favored localities, where a crop can
be obtained perhaps two years or three years in five. But with a minute
knowledge of the climatic conditions, and with methods adapted to