region lying between the Rocky Mountains
upon the east and the Sierra Nevada Mountains upon the west. To the
south lay the Grand Canon of the Colorado, while upon the north
the boundary was formed by the canons of the Snake and Columbia
rivers.

After a time it was found that this region, covering about two
hundred and twenty-five thousand square miles, not only was extremely
dry, but had no outlet to the ocean. A rim of higher land all about
made of it so perfect a basin that it became known as the Great
Basin. None of the water that falls upon the surface of this basin
ever reaches the ocean through surface streams. Some of it soaks
into the rocks, but the greater part is evaporated into the dry
air.

We have already learned something about the way in which the ridges
and hollows of the earth's surface are made. We have learned of
the wrinkling of the crust, of the formation of fissures, and of
the erosive work of running water. The interesting features of
the Great Basin are mainly the result of two causes: the sinking
of a portion of the earth's surface, and the lack of rainfall.

Long ago the Wasatch Range of eastern Utah and the Sierra Nevadas
of California formed parts of a vast elevated plateau. Then there
came a time when the forces holding up the plateau were relaxed,
and as the weight of the plateau pressed it down, the solid rocks
broke into huge fragments. Some of the blocks thus made sank and
formed valleys; others were tilted or pushed up and formed mountains.
Thus the north and south mountain ranges and valleys of the Great
Basin were born.

We must understand, then, that the Great Basin is not a simple
depression with higher land all about. The breaking up of the surface
produced many basins, large and small. Some of these basins are six
thousand feet above the level of the sea, others are much lower,
and one has been dropped below the level of the sea, so that if it
were not for barriers the water would flow in. Some of the basins
are rimmed all about by steep mountains, others are so broad and
flat that it is difficult to tell that they really are basins.
Many of the valleys are so connected with one another that if a
heavy rainfall should ever occur drainage systems would be quickly
established.

The Great Basin now appears like the skeleton of a dried-up world; but
if the climate should change and become like that of the Mississippi
Valley, the surface of the desert would undergo a wondrous