On October 15, 1956, President Dwight D. Eisenhower pressed a button on his desk in Washington, D.C., sending a telegraph signal that set off the first blast of dynamite at the portal of the right diversion tunnel. Drilling the tunnels through the porous Navajo sandstone abutting the dam site posed major problems for the excavation crews of the Mountain States Construction Company, which won the contract for the diversion tunnels in 1956. Transporting workers and equipment to the bottom of the canyon was extremely difficult. Initially, transport was done by barge from Wahweap Creek, but the fast current of the Colorado River could be dangerous. After a barge capsized, spilling tons of machinery into the river, a much safer cable-car system was installed. During excavation, the rock frequently broke apart or "slabbed" and collapsed into the tunnels, and metal bolts had to be drilled into the rock to secure it. The largest such event, on August 5, 1958, sent crashing down onto the upper portal of the left diversion tunnel.