All the foregoing dams are built of dry rubble stone and faced with a water-tight lining of planks.
The
Tuolumne County Water Company has built several timber crib dams, the
largest of which is across the south fork of the Stanislaus River. This
dam, which is three hundred feet long and sixty feet high, rests for
its entire base on solid granite bed-rock. The cribs, constructed of
round tamarack logs from two to three feet in diameter, are about
eight feet square from log to log (ten feet centre to centre), and the
timbers are pinned together with wooden treenails. The cribs have no
rock filling.
The
face is formed of flattened three-inch timber pinned with wooden
treenails to the crib and calked with cedar bark. The flood water
passes over the crest of the dam for the entire length. The water is
drawn off by several gates, one above the other, placed on the inclined
water-face. The dam was built in 1856. Its total cost did not exceed
$40,000. Pine dams owned by this company, constructed on the same
plan, have decayed, while cedar cribs are still in perfect order. The
Spring Valley and Cherokee Company's Concovv reservoir in Butte County
is formed by two earthen dams, each about fifty-five feet in height;
one of these, which is used as a waste, has its lower side built of
heavy brush embedded in the earth.
THE BOWMAN RESERVOIR AND DAM.
This
reservoir was designed for the supply of water during the dry season of
the year to the gravel mines operated by the North Bloomfield Mining
Company. It is located in a mountain valley, on Big Canon Creek, a
branch of the Yuba River.
It
is fed from a gross catchment area of 28.94 square •miles. Higher up on
the same stream there are several other reservoirs owned by the
Bloomfield and Eureka Lake companies, the upper one (Eureka Lake
reservoir) holding 661,000,000 cubic feet of water. In ordinary seasons
