Horseshoe Dam?

Does anyone knows if they shot the interior of the Horseshoe Dam on location or did they used a power station near L.A.? As this was a Katzman production it's probably safe to assume the latter! Obviously they used scale models of the dam as it blows up.

And if it was indeed shot in and around L.A. where exactly was that?

The interior of the plant appears immense and pretty impressive, gotta wonder if it still exists today or is another victim of Gore-ism (or is that Gore-itis?) Thanks!