But take a look closely at the back photo. The adoring fans rushing the stage while one of the Dog Nights moves closer. The stage, obviously is from a well trodded permanent stage at another venue. Arenas didn't have wood floor stages like that. Security at The Forum would probably have beaten those teenage girls to a pulp. Chances are nobody was even paying much attention to the opening act. The venue was probably not even full by that time. My hunch is that this photo was probably taken at the much smaller general admission Hollywood Palladium. In fact, I doubt that any of the photos, save for the ones with the house lights on, are from the Forum gig.
And a side note, Chuck Negron lives up the street from me in Sherman Oaks. Read his book - Three Dog Nightmare.