Morris Dam, in San Gabriel Canyon a few miles North of Azusa, was built in the 30's. The spillway is rarely in use like in the photo. San Gabriel Dam, further up the canyon, was later constructed to contain sediment which would otherwise be carried into Morris Reservoir.
The reservoir behind the dam has been used by the Navy for decades to test torpedoes and other weapons. I remember the area being closed to public use and well patrolled. With no fishing pressure, huge trout were known to be in the lake. A friend of mine went fishing there several times; when apprehended the guards would kick him out and impound his fishing equipment. So, he always brought old fishing gear he didn't mind losing when sneaking in to go fishing.
One time when the spillway was in use, like in the photo, I went fishing in the normally dry streambed below the dam and caught a 22" rainbow trout. Good times!