Seventy-five years ago today, on July 9, 1948, 20 tons of explosives were used to bring down a granite hill in Missing Gorge in what was then a record for a commercial blast in the county. Rocks blasted loose from the quarry site in Mission Gorge were hauled 15 miles west to construct the jetties at the mouth of Mission Bay.
From the San Diego Union, Saturday, July 10, 1948:
20-TON POWDER BLAST RIPS MOUNTAIN TO BITS
By Clyde V. Smith
The earth shook a little, there was a “whoomph” and a mountain of granite fell to pieces.
The sound of the explosion–reportedly the largest ever set off in San Diego County–was not nearly as impressive as the roar that followed when an estimated 90,000 to 124,000 tons of rock, in pieces from the size of a large house to a pebble, crashed down yesterday afternoon into Mission Gorge, 15 miles east of San Diego in Mission Valley.
HOISTED BY POWDER
Twenty tons of powder, placed in seven separate charges far back in the mountain tunnels, were set off simultaneously by Joe P. Mardis, hiding in another tunnel 100 yards west of the blast area, pushed the batter plunger at 4:30 p.m. The mountain bulged and disintegrated.
More than 100 spectators, watching from a hot, bare, brown knoll across a gully from the blast center, saw a large rusty-colored cloud of granite dust billow from the torn mountain. The gray acrid smoke of the powder lingered over the rock. The blast cut straight and clean, leaving a sheer wall in the granite mountain.
MATERIALS FOR JETTIES
Granite blasted loose from the mountain will be hauled by truck to construct three jetties at the mouth of Mission Bay.
Before the dynamite was exploded yesterday, weeks of preparation had gone into the job. Thirty-five workmen of the Macco Corp., in charge of the quarrying job, had tunneled 60 feet directly into the hill, with branches off at right angles, one extending 100 feet and the other approximately 80 feet.
Beginning Monday night, miners working in three shifts began filling “pockets” in the tunnel with 40,000 pounds of explosives, packing the rest of the tunnel solidly with sandbags.
BIG TASK AHEAD
E.P. Davies, Macco superintendent, estimated the granite torn loose by yesterday’s blast would provide enough material to keep the trucks busy for 90 days, hauling it to the Mission Bay project. Pieces of the rock will have to be broken again. The largest chunks will weigh 300 or 400 tons, Davis estimated.
Already the Macco crews have begun tunneling for an even larger blast. Davies said probably more than 50,000 tons of powder would be set off next time, tentatively scheduled Sept. 10, in a hill just west of yesterday’s Mission Gorge explosion. Davies and Ben Early, of San Francisco, explosives engineer for the Hercules Powder co., supervised preparations.
Excitement gripped the perspiring spectators as a shrill whistle sounded a warning 5 minutes before the explosion. when the final whistle blew and the mountain went up, many who had wanted to catch the scene on film snapped their camera shutter too quickly to catch the full effect of the blast.
