THE GREAT VALLEY OF CALIFORNIA.
General Topography.—The
valleys of the Sacramento and the San Joaquin rivers form in the
centre of California a large plain, nearly elliptical in shape,
extending from near Shasta, in lat. 400 40' N., to Fort Tejon, in lat. 340
50' N., an extreme length of four hundred and fifty miles, with an
average width of forty miles, and an area of eighteen thousand square
miles.
This
plain is comparatively level. The Sacramento River, between Shasta and
its mouth, has an average fall of 2.8 feet per mile. The San Joaquin
River, from Kern Lake to its outlet, has an average inclination of 1.1
feet per mile. The valley of the Sacramento is narrower than that of
the San Joaquin. The southern portion of the latter is very level and
contains several shallow lakes of considerable area. The evaporation
here about equals the water supply.
Drainage.—By
far the larger part of the water coming into the Great Valley is
derived from the Sierra Nevada. There is hardly a stream which
furnishes water throughout the year on the east slope of the Coast
Ranges, certainly not one in the San Joaquin division. The fact that
many rivers, passing chiefly through the mining regions, flow down the
west slope of the Sierra and empty into the Sacramento or San Joaquin,
makes the whole drainage system worthy of attention.
Rainfall.—The
rainfall of the Great Valley is comparatively small, especially in the
southern parts. On the east slope of the Coast Ranges the amount of
water derived from rain is small. On the west slope of the Sierra
there is considerable precipitation, chiefly in winter, and in great
part in the shape of snow. In the spring and early summer the flow of
water down the last mentioned slope is greater than at other seasons,
so much so that every year freshets occur. Heavy storms often cause
destructive floods here, and if the theories of many
