20 LANDS OF THE ARID REGION OF THE UNITED STATES. 
dependent on latitude and altitude; the higher the latitude the better are 
the grasses, and they improve as the altitude increases. In very low alti- 
tudes and latitudes the grasses are so scant as to be of no value; here the 
true deserts are found. These conditions obtain in southern California, 
southern Nevada, southern Arizona, and southern New Mexico, where broad 
reaches of land are naked of vegetation, but in ascending to the higher 
lands the grass steadily improves. Northward the deserts soon disappear, 
and the grass becomes more and more luxuriant to our northern boundary. 
In addition to the desert lands mentioned, other large deductions must be 
made from the area of the pasturage lands. There are many districts in 
which the ‘country rock” is composed of incoherent sands and clays; 
sometimes sediments of ancient Tertiary lakes; elsewhere sediments of 
more ancient Cretaceous seas. In these districts perennial or intermittent 
streams have carved deep waterways, and the steep hills are ever washed 
naked by fierce but infrequent storms, as the incoherent rocks are unable to 
withstand the beating of the rain. These districts are known as the mau- 
vaises terres or bad lands of the Rocky Mountain Region. In other areas 
the streams have carved labyrinths of deep gorges and the waters flow at 
great depths below the general surface. The lands between the streams 
are beset with towering cliffs, and the landscape is an expanse of naked 
rock. ‘These are the alcove lands and canon lands of the Rocky Mountain 
Region. Still other districts have been the theater of late voleanic activity, 
and broad sheets of naked lava are found; cinder cones are frequent, and 
scoria and ashes are scattered over the land. These are the lava-beds of 
the Rocky Mountain Region. In yet other districts, low broken mountains 
are found with rugged spurs and cragey crests. Grasses and chaparral 
grow among the rocks, but such mountains are of little value for pasturage 
purposes. 
After making all the deductions, there yet remain vast areas of valua- 
ble pasturage land bearing nutritious but scanty grass. The lands along 
the creeks and rivers have been relegated to that class which has been 
described as irrigable, hence the lands under consideration are away from 
the permanent streams. No rivers sweep over them and no creeks meander 
among’ their hills. 
