Don,

That might be the nicest view of the Knight's Ferry Bridge I've ever seen. The construction technique IS very similar -- I wonder if it was built by the same company?
....all the gas blew east up-canyon.
And it didn't dissipate over that distance -- Yeah, that would have been very surprising to be swimming in the pool and getting gassed.

Hint #2: The Knight's Ferry Bridge is two years older than the subject of this puzzle.... and they share at least one more common element....

Mark