San Francisco flooded one of Yosemite’s most beautiful valleys, and less than 1% of visitors ever go see what’s left
San Francisco needed drinking water, and Yosemite National Park had a valley in the way. So in the early 1900s, the city flooded it — a valley John Muir spent years insisting was every bit as beautiful as Yosemite Valley itself.
He wasn’t alone. The fledgling Sierra Club and newspapers across the country rallied against the plan, but Congress passed the Raker Act in 1913 anyway. President Woodrow Wilson signed off on damming inside a national park, and it became the first major conservation fight to play out on a national stage in U.S. history — one conservationists lost.
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Crews broke ground on O’Shaughnessy Dam in 1919, and by 1938 it stood 430 feet tall, holding back a reservoir that swallowed the valley floor under roughly 300 feet of water. What’s left above the surface is dramatic: sheer granite walls rising straight out of blue-green water, with waterfalls still dropping in from hundreds of feet up.
Hetch Hetchy isn’t even connected to the rest of Yosemite National Park by road — it has its own separate entrance station off Highway 120, open daylight hours only. Most people who drive into the park never make the detour.
According to the National Park Service, less than 1% of Yosemite’s roughly four million annual visitors ever go. That’s the entire appeal: the same kind of granite drama as the Valley, minus the crowds circling for a parking spot.
The main trail follows the reservoir’s north shoreline out to Wapama Falls, a 4.6-mile round trip with about 954 feet of climbing that AllTrails rates easy. Dogs aren’t allowed, and the exposed, rocky footing makes it feel like more effort than that number lets on.
One thing worth knowing before you go: Wapama Falls and its neighbor, Tueeulala Falls, both run on snowmelt, so by August they can shrink to a trickle or dry up completely. If you want them roaring — and you will get soaked crossing the footbridges underneath — plan the trip for April through June instead.
Right now, the payoff is still the valley itself: the dam, the cliffs, and the waterfalls that have carved this basin since long before anyone thought to flood it. Swimming and boating are both off-limits, since this reservoir still supplies San Francisco’s drinking water — fishing from shore is the one exception.
A standard Yosemite pass covers the entrance — $35 per vehicle, good for seven days — and an America the Beautiful annual pass works here too, since Hetch Hetchy still sits on federally managed national park land.
Skip the fight for a parking spot in Yosemite Valley on this one trip, and go find the version of the park almost nobody bothers to look for anymore.
Would you make the detour for a valley most visitors don’t even know is still there?
Trip tips: grab a rental car to get out here, lock in your hotel before the good rooms are gone, or skip both and book a camper van instead.
Rules and fees change — always confirm current requirements before you go.
