Bear Gulch Reservoir, Pinnacles National Monument, California, USA.
I bought a strip of souvenir slides at the gift shop on the way out, because they included a slide of the fateful pond. Like all such slides they were duplicated sometime in 1943 or so on archivally unstable film. The above was the best I could make it look with some pretty drastic colour gamma changes.
Trust me, the actual place looks much nicer than this.
Back to the wet camera story