Hetch Hetchy Valley Before the Dam

Here is a map of the Hetch Hetchy Project which in 1934 began to deliver water 167 miles west to San Francisco. Map by Shannon1 and from Wikimedia Commons.

As a hiker in California, I always heard that Hetch Hetchy Valley was just as spectacular as Yosemite Valley before it was dammed in 1923 to provide water for San Francisco. But I always wondered exactly what it looked like.

Hetch Hetchy Valley from roughly the same place as the picture above, in 2002. Picture © Daniel Mayer.

Compared with Yosemite Valley, the walls of Hetch Hetchy are smoother and rounder. Yosemite Valley, in contrast has extremely ragged walls, with many pinnacles and spires projecting upward. This is because the Tuolumne catchment basin above Hetch Hetchy is almost three times as large as the catchment basin of the Merced River above Yosemite. While both valleys were filled with ice about a million years ago, they were not both filled completely in later glaciations. During the last glaciation (about 20,000 years ago) Hetch Hetchy Valley was completely filled with a glacier that scoured the heck out of it. Yosemite Valley, however, was only partially filled with ice, and thus the higher elevations we see today were not re-scoured.