asp. Responding to increasing
pressures from below, the continent was folding from north to south. The
miracle of the making of the Rockies was enacting.

During all of Tertiary times earth movements of tremendous energy rocked
and folded the crust and hastened change. The modern Sierra rose upon
the eroded ruins of its predecessor, again shutting off the
moisture-laden western winds and turning the southwest again into a
desert. One of the mountain-building impulses spread eastward from the
Sierra to the Wasatch Mountains, but Nature's project for this vast
granite-cored tableland never was realized, for continually its central
sections caved and fell. And so it happened that the eastern edge of the
Sierra and the western edge of the Wasatch Mountains became the
precipitous edges, thousands of feet high, of a mountain-studded desert
which to-day is called the Great Basin. It includes southeastern Oregon,
nearly all of Nevada, the western half of Utah, and a large area in the
south of California, besides parts of Idaho and Wyoming. It is 880 miles
north and south and 572 miles wide. Its elevation is five thousand feet,
more or less, and its area more than two hundred thousand square miles.

This enormous bowl contained no outlet to the sea, and the rivers which
flowed into it from all its mountainous borders created a prehistoric
lake with an area of fifty-four thousand square miles which was named
Lake Bonneville after the army officer whose adventures in 1833 were
narrated by Washington Irving; but it was Fremont who first clearly
described it. Lake Bonneville has evaporated and disappeared, but in its
place are many salty lakes, the greatest of which is Great Salt Lake in
Utah. Attenuated rivers still flow into the Great Basin, but are lost in
their sands. The greatest of these, the Mohave River, is a hundred miles
long, but is not often seen because it hides its waters chiefly under
the surface sands. Lake Bonneville's prehistoric beaches exist to-day.
Transcontinental passengers by rail cross its ancient bed, but few know
it.

The Great Basin to-day is known to travellers principally by the many
lesser deserts which compose it, deserts separated from each other by
lesser mountain ranges and low divides. Its southern and southeastern
boundaries are the plateaus and mountains which form the northern
watershed of the muddy Colorado River and its confluents. South of the
Colorado, the plateaus of New Mexico, Arizona,