than to quarry from the cliffs nearer the dam. Hence, the supply of material being abundant, flat slopes of 450 for
the wall were adopted, which allowed very much lighter face walls to be
used with safety than would have been the case had they been more
nearly vertical.
The
stone for these face walls was quarried from solid rock, and cost in
place three or four times more than the loose stone brought from the
mountain side. When in the future the timber logs forming the cribs in
the original seventy-two feet dam decay, there will be some slight
subsidence of the superincumbent stone. The depth of the stone is so
considerable and the slopes of the walls are so flat that it is
believed this subsidence will not be noticeable.
Waste Dam.—Figures
6A and 6B show longitudinal and cross sections of the waste dam. This
is a crib of round cedar timbers varying from twelve to thirty inches
in diameter, notched down to heart wood at the joints, and firmly
bolted with three-quarter and one-inch drift bolts. The foundation logs
are all fastened to the bedrock with one and one-half inch bolts.
The
cribs are solidly filled with granite rocks varying from several tons
to a few pounds. No sand or fine stone was used in this filling. A
plank facing of three-inch heart sugar-pine is spiked on the
water-face, making a water-tight lining similar to that on the main
dam.
The
crest of the original dam is ninety-two and one-half feet above datum
line, being four feet lower than the summit of the main dam. A light
superstructure of four feet allows the water to be raised to the height
of the main dam. The waste dam is provided with twenty-eight escapes,
each four feet wide and eleven feet deep. These waste-ways are closed,
when all danger from freshets is passed, with boards two inches thick,
eight inches wide, four and one-half feet long, laid horizontally, and
sliding to their places one above the other on the inclined
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