There are pictures of Mountain Lake Park at sfpl.lib.ca.us/librarylocations/sfhistory/browse.htm Scroll down to "Parks," click "M."
I had countless hours of fun and adventure in that park when I was a kid during WWII. Friends from Sutro School and I sailed toy boats on the lake or played with model war planes cut from the back of Wheaties breakfast cereal boxes or bought at the 5 and 10 on Clement. Huge Navy blimps occasionally flew over, and when we heard aircraft engines we looked up to see how many combat craft we could identify. The “keenest” was the huge B-29 Superfortress bomber. We felt proud that the war stamps we bought at school every Friday with our nickels and dimes helped to pay for planes like that.
We played hide and seek, cowboys and Indians, and fiercely battled each other through the brush up and down hills we might call Saipan, or Iwo Jima, places we had seen in newsreels at Saturday afternoon matinees at the Coliseum Theatre. In the Marine Hospital that was on the hill just west of the park were horribly wounded men who had fought in real battles on those islands and in other areas of the Pacific.
Before heading home it was necessary to stop at a small store at California and 11th for a treat, a 5c Coke or candy bar. This was a wonderful end to a wonderful day at the park.