Men in canyon tunnels preparing to set explosives for blasting excavation during construction of San Gabriel Dam. Reported in "GIGANTIC BLAST AIDS DAM WORK: Ninety Tons of Powder Used at San Gabriel Side of Canyon Seems Molten Before Explosive Engineering Feat Figured to Exact Result," Los Angeles Times, 27 Jun. 1929: A10.
Cloud of dust and debris cascading down San Gabriel Canyon wall after explosion during construction of San Gabriel Dam. Reported in "GIGANTIC BLAST AIDS DAM WORK: Ninety Tons of Powder Used at San Gabriel Side of Canyon Seems Molten Before Explosive Engineering Feat Figured to Exact Result," Los Angeles Times, 27 June 1929: A10.
Reported in "GIGANTIC BLAST AIDS DAM WORK: Ninety Tons of Powder Used at San Gabriel Side of Canyon Seems Molten Before Explosive Engineering Feat Figured to Exact Result," Los Angeles Times, 27 June 1929: A10.
Reported in "GIGANTIC BLAST AIDS DAM WORK: Ninety Tons of Powder Used at San Gabriel Side of Canyon Seems Molten Before Explosive Engineering Feat Figured to Exact Result," Los Angeles Times, 27 June 1929: A10.
Workers at the bottom of the canyon at the Pacoima Dam site working on wood framing and concrete pouring. Men in suits and women wearing dresses and sun hats observe.
ANSWER: Yep, it's the spillway of Hansen Dam. (Didn't you notice those foothill peaks peeking through the opening?) And sure, it's racy. They have outboard motorboat races on the lake behind it and sports car races on a track directly below it.