This photograph was taken from atop the O'Shaughnessy Dam and overlooks the Hetch Hetchy Reservoir.
In it you can see both the Tueeulala (upper left) and Wapama (center left) Falls. Hetch Hetchy Dome and Holana Rock are reflected in the slightly icy water.
The visible part of the reservoir makes up less than 20% of its area.
This reservoir was created (against the wishes of John Muir) partly as a means to assure a water supply for San Francisco after the debacle of the 1906 eartquake and subsequent fires.
This is an area worthy of further photographic exploration!