ids, gathering the fruit
and delivering it at the nearest railroad point.

Mining is carried on only in the mountains which rise above the
lava flood, for the mineral veins are for the most part older than
the lava of the plateau. We are certain that many very valuable
deposits of the precious metals lie buried beneath the lava fields.

It is thought that the volcanic history of the Columbia plateau
has been completed. Now the streams are at work carrying away the
materials of which it is composed and may in time uncover the old
buried land surface.

THE CANONS OF THE SIERRA NEVADA MOUNTAINS

The western half of our country contains the deepest and most
picturesque canons in the world. Those of the Colorado and Snake
rivers form trenches in a comparatively level but lofty plateau
region. The canons of the Sierra Nevada Range, on the contrary,
take their rise and extend for much of their length among rugged
snowcapped peaks which include some of the highest mountains in
the United States. All these canons are the work of erosion. The
rivers did not find depressions formed ready for them to occupy,
but had to excavate their channels by the slow process of grinding
away the solid rock.

The streams of the Sierra Nevada mountains begin their course in
steep-walled alcoves under the shadows of the high peaks, where
they are fed by perpetual snow-banks. Soon they bury themselves
between granite walls, which at last tower three thousand feet
above their roaring waters. After many miles the canons widen,
the walls decrease in height, and the streams come out upon the
fertile stretches of the Great Valley of California.

Nature works in many ways. Her tools are of different kinds, but
the most important one is running water. The forms which she produces
are dependent upon the kind of rock upon which she works. Where
the surface of the earth is soft the results of her labor are not
very interesting, but if the crust is hard the forms which she
produces are often so remarkable that they arouse our wonder and
admiration.

[Illustration: FIG. 12.--SAN JOAQUIN RIVER EMERGING UPON THE PLAIN
OF THE GREAT VALLEY]

In shaping the Sierra Nevada mountains Nature had a grand opportunity.
Here she produced the Yosemite Valley, which has a setting of cliffs
and waterfalls that attract people from all over the world. Hetch-Hetchy
Valley at the north of the Yosemite, and Tehipite and King's River
canons at the south, are inter