The field meet scenes were filmed at an old Southern California motorcycle racing venue called Crater Camp, later changed to Crater Bowl. It was right off Topanga Canyon Road on the Valley side. I spectated at a race there once and I think it closed in about 1960. I will assume there are big fancy homes there now.
I'm not sure, but I think the street riding scenes were filmed on Ventura Boulevard west of the San Fernando Valley. That used to be THE way to get from L.A. to Ventura and beyond before the 101 (Ventura) Freeway. Of note are the tank-shift Indian and the complete disregard for traffic laws that put us motorcyclists in such good stead with the law and the general populace for so long. This clip ends about how you think it will as Harley-Davidsons emerge victorious. Heh. Enjoy.