Looking at the pics and the area which it was found, and the frame number,plus the tangs on the bottom bracket,,,I would hazard a guess and say it was one of mine, I sold quite a few in the Stockton California district in about the 1975's....just guessing though, if it becomes a headache, toss it back into the dumpster and buy a new one..
COLIN LAING...Sunny Chandler,,AZ,,USA