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When men were able to find work in the first phase of the dam construction it was occasionally on an auxiliary project
such as building rail lines to the dam. Most men, however, found themselves working on the construction of the diversion
tunnels. Before the dam could be built, the Colorado River needed to be temporarily diverted from its course.
Four tunnels were planned, two on each side of the river. The most difficult part of the entire project, the construction of
the diversion tunnels began May 12, 1931 and was scheduled to be completed before October 1, 1933. As Six Companies would be
fined for every day the diversion tunnels went over schedule, the excavation of the tunnels proceeded at a furious pace.
When completed, the diameter of each tunnel would measure 50 feet
wide, 3/4 of a mile in length. The mechanics of drilling into the
solid rock walls of Black Canyon did not daunt dam foreman, Frank
Crowe. Knowing that it would take countless men to make even an
inch of headway into the walls, Frank Crowe came up with an idea
that would allow over twenty men to drill at once. This invention,
called a jumbo, consisted of rows of platforms built atop a truck.
Men would stand on the platforms to drill and tamp blasts into the
rock.
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