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San Francisco-Oakland Bay Bridge
Over the west bay between San Francisco and
LYerba Buena Island at twin suspension bridges, each
4,630 feet long, joined end to end and having at their junc-
tion a common anchorage consisting of a great concrete
monolith, topped by a steel shroud, which rises 282 feet
above water and rests on bedrock 220 feet below low tide.
The theory of the suspension bridge is that of the clothes-
line anchored at either end, sufficient to hold the weight
hung thereon, and supported at intervals by props or towers.
The piers of this bridge-51 in number-set new marks
on engineering frontiers, going deeper below water than
any previous substructure has heretofore been built. Some
of the piers go as far as 237 feet below low tide.
The two suspension bridges have 2,310-foot main spans.
The lower deck carries two tracks for interurban electric
cars and three lanes for heavy trucks, and the upper deck
carries a 58-foot highway for six lanes of automobiles.
PICTURE No. 10-A PUB. BY J. C. BARDELL SAN FRANCISCO, CALIFORNIA
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