d all northwestern Utah; to this former
body of water the name Bonneville has been given, in honor of a noted
trapper. Pyramid, Winnemucca, Carson, Walker, and Honey lakes, now
separated from one another by sagebrush deserts, were then united
in one great lake, to which the name Lahontan has been given, in
honor of an early French explorer.

[Illustration: FIG. 42.--MONO LAKE, CALIFORNIA]

Lake Lahontan covered a large portion of northwestern Nevada and
penetrated into California. It was broken into long winding arms
and bays by various mountain ranges. The deepest portion of this
ancient lake is now occupied by Pyramid Lake, which is, perhaps,
the most picturesque of all the Basin lakes. Fish can live in the
waters of this lake, although nearly all the others are so salty
or so alkaline that they support none of the ordinary forms of
life.

[Illustration: FIG. 43.--ROUND HOLE, A SPRING IN THE SMOKE CREEK
DESERT

Bed of old Lake Lahontan]

Upon the Black Rock Desert, in northern Nevada, there are large
springs once covered by Lake Lahontan, in which fish are found.
It is thought that the ancestors of these fish must have been left
there at the time of the drying up of the water.

After the Glacial period the present arid climate began to prevail
in the land. Hundreds of the shallow lakes which had been scattered
over this extensive region disappeared. Others contained water for
only a portion of each year. A body of water which is not permanent,
but comes and goes with the seasons, we call a playa lake. Many of
these playa lakes present in summer a hard, yellow-clay floor of
many miles in extent and entirely free from vegetation. The beds
of others are covered with a whitish crust, formed of the various
salts which were in solution in the lake water.

[Illustration: FIG. 44.--ROGERS LAKE, MOHAVE DESERT

A playa lake]

An important feature of the lakes of the Great Basin is the presence
of large quantities of such substances as common salt, soda, borax,
and nitre. The ocean is salt because it has no outlet, while the
rivers of the globe are continually bringing into it various minerals,
dissolved from the rocks over which they flow. Lakes with outlets
are not salty, because with a continuous change of the water there
is no opportunity for the minerals to accumulate, although they
are always present in small quantities. Any lake which does not
receive enough running water to cause it to overflow the borders