The high plains of this soil district are
often spoken of as the Palouse country. The soils of the western
part of this district are of basaltic origin; over the southern part
of Idaho the soils have been made from a somewhat recent lava flow
which in many places is only a few feet below the surface. The soils
of this district are generally of volcanic origin and very much
alike. They are characterized by the properties which normally
belong to volcanic soils; somewhat poor in lime, but rich in potash
and phosphoric acid. They last well under ordinary methods of
tillage.
_The Great Basin.--_The third great soil district is included in the
Great Basin, which covers nearly all of Nevada, half of Utah, and
takes small portions out of Idaho, Oregon, and southern California.
This basin has no outlet to the sea. Its rivers empty into great
saline inland lakes, the chief of which is the Great Salt Lake. The
sizes of these interior lakes are determined by the amounts of water
flowing into them and the rates of evaporation of the water into the
dry air of the region.
In recent geological times, the Great Basin was filled with water,
forming a vast fresh-water lake known as Lake Bonneville, which
drained into the Columbia River.
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