Hetch Hetchy
Valley Reservoir and valley in Yosemite National Park
In Yosemite National Park’s northwestern reaches, Hetch Hetchy draws hikers to a dammed valley, reservoir and waterfalls along the Tuolumne River. Visitors come for day hikes, backcountry camps and quieter granite scenery compared with Yosemite Valley.
Hetch Hetchy is a river valley and reservoir complex in the northwestern part of Yosemite National Park in California, formed when the Tuolumne River was impounded behind O’Shaughnessy Dam in the early 20th century. The site is notable for its engineered reservoir within a formerly glaciated valley.
Trail routes run along the reservoir and into the surrounding canyon and provide views of seasonal waterfalls and steep granite walls. The most-visited trail sections give close views of the dam, reservoir shoreline, and several falls that are prominent in spring runoff.
The valley was dammed following passage of the Raker Act in 1913; construction of O’Shaughnessy Dam proceeded in the 1910s and early 1920s and permanently flooded the natural valley. Since then the reservoir has been operated to provide water and hydroelectric power to the city of San Francisco and surrounding areas.
Hetch Hetchy sits in the upper Tuolumne River watershed inside Yosemite National Park, in the western Sierra Nevada. The site is reached by the park road off the Hetch Hetchy entrance and lies in a deep canyon carved into granite within the park boundaries.
- Water supply history: The Raker Act of 1913 authorised construction of waterworks in the valley; the dam and reservoir were completed in the early 1920s to supply San Francisco.
- Access and best time: Access is by park road and trail from the Hetch Hetchy entrance within Yosemite National Park; trails along the reservoir are typically busiest in late spring when waterfalls are at peak flow.
What to See #
- O'Shaughnessy Dam: The concrete gravity O'Shaughnessy Dam impounds the Tuolumne River to form the reservoir and was completed in the early 1920s following federal approval in 1913.
- Hetch Hetchy Reservoir: Hetch Hetchy Reservoir created by the dam, lying in the Tuolumne River canyon inside Yosemite National Park and impounded behind O'Shaughnessy Dam.
- Trails and waterfalls: Several seasonal waterfalls and canyon-side trails, notably the trail running along the reservoir to views of waterfalls such as Wapama Falls during high runoff.
How to Get to Hetch Hetchy #
Hetch Hetchy is accessed from the Hetch Hetchy Road off of Highway 120/Big Oak Flat Road in Yosemite National Park. From Yosemite Valley it’s about a 1-1.5 hour drive (roughly 45-60 miles depending on route). The nearest major gateway towns are Groveland and Jamestown on the west side; check NPS road conditions in winter, when Hetch Hetchy Road is often closed.
Tips for Visiting Hetch Hetchy #
- Drive Hetch Hetchy Road early in the morning; the narrow canyon shade and low-angle light make the waterfalls and the O'Shaughnessy Dam more photogenic before mid-day.
- If walking the Wapama Falls / Rancheria Falls loop, bring warm layers-even summer mornings on the reservoir can be chilly and windy.
- Look for subtle scars of human engineering: the concrete lip of O'Shaughnessy Dam, the old metal catwalks, and the polished handrail at the Wapama bridge all have small graffiti and wear that tell the water story most guidebooks skip.
Best Time to Visit Hetch Hetchy #
A reservoir and canyon inside Yosemite National Park formed when O'Shaughnessy Dam was completed in 1923; access follows a road and a handful of trails into one of the park's quieter, more controversial corners.
Weather & Climate near Hetch Hetchy #
Hetch Hetchy's climate is classified as Hot-Summer Mediterranean - Hot-Summer Mediterranean climate with warm summers (peaking in July) and cold winters (coldest in December). Temperatures range from -1°C to 31°C. Moderate rainfall (901 mm/year) with a pronounced dry season.
January
January is cold with highs of 10°C and lows of 0°C. The wettest month with heavy rain (152 mm) and partly cloudy skies.
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February
February is cold with highs of 12°C and lows of 0°C. Significant rainfall (147 mm) and partly cloudy skies.
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March
March is cold with highs of 14°C and lows of 1°C. Significant rainfall (128 mm) and partly cloudy skies.
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April
April is cool with highs of 17°C and lows of 3°C. Moderate rainfall (77 mm) and partly cloudy skies.
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May
May is cool with highs of 22°C and lows of 7°C. Moderate rainfall (32 mm).
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June
June is mild with highs of 26°C and lows of 10°C. Light rainfall and clear sunny skies.
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July
July is the warmest month with highs of 31°C and lows of 13°C. The driest month with just 6 mm and clear sunny skies.
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August
August is mild with highs of 31°C and lows of 13°C. Almost no rain and clear sunny skies.
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September
September is mild with highs of 28°C and lows of 11°C. Light rainfall and clear sunny skies.
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October
October is cool with highs of 22°C and lows of 6°C. Moderate rainfall (51 mm) and mostly sunny skies.
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November
November is cold with highs of 14°C and lows of 1°C. Significant rainfall (133 mm).
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December
December is the coolest month with highs of 10°C and lows of -1°C. Significant rainfall (130 mm) and partly cloudy skies.
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