I cant speak for California water treatment plants but most WW2 guard guns would have been one of the following pump shotguns, Stevens 520-30 (the most common, a John Browning designed pump with an A5 type hump back), Stevens 620 (same gun more or less with a rounded receiver), Winchester Model 12 or Model 97, Ithaca 37. All of these were built in both trench (bayonet lug and heat shield) or riot configuration with out the hardware on the muzzle end.
The Remington Model 11 auto was also issued but only as a riot gun although there were a small amount of WW1 trench guns made of this model as well.
Hope this helps.
Last edited by Lawrence Kotchek; 08/28/09 11:57 PM.