ide--in this case the western one--the slope was long
and gentle, while upon the east it was very abrupt.

[Illustration: FIG. 14.--THE YOSEMITE VALLEY]

Nature, the sculptor, took this mountain block in hand, and with
the aid of running water began to carve its surface into a most
intricate system of canons and ridges. The streams first flowed
over the easiest slopes to the Great Valley of California, but
soon they began to cut their way down into the granite, while along
the crests of the ridges the more resistant rocks began to stand
out as jagged peaks.

Thus Nature worked until the mountains promised before long to be
well worn down. The canons had widened to valleys and the rugged
slopes had given place to gentle ones. Toward the northern end of
the range the work was even farther advanced, for the streams,
now choked with gravel and sand, flowed over broad flood plains.
In this gravel was buried a part of the wealth of California. The
rocks over which the streams flowed contained veins of quartz with
little particles of gold scattered through it, and as the surface
rock crumbled and was worn away, the gold, being much heavier,
slowly accumulated in the gravel at the bottom of the streams.
This gold amounted in value to hundreds of millions of dollars.

The forces within the earth became active again. Apparently Nature
did not intend that the gold should be forever buried, or that the
country should always appear so uninteresting. Internal forces
raised the mountain block for a second time, tilting it still more
to the westward. Volcanoes broke forth along the summit of the
range near the line of fracture, and floods of lava and volcanic
mud ran down the slopes, completely filling the broad valleys of
the northern Sierras and burying a great part of the gold-bearing
gravel.

The eruptions turned the streams from their channels, but on the
steeper slope of the mountains the rivers went energetically to
work making new beds. They cut down through the lava and the buried
gravel until they finally reached the solid rock underneath. Into
this rock, which we call "bed-rock," they have now worn canons
two thousand feet deep. The beds of gravel that lay under the old
streams frequently form the tops of the hills between these deep
canons. Here they are easily accessible to the miners, who by tunnels
or surface workings have taken out many millions of dollars' worth
of gold.

The important canons of the northern S