Qualla: O'Shaughnessy Dam

O'Shaughnessy Dam: Introduction

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit User:Inklein, CC BY-SA 3.0. John Muir died ten days after construction began on the dam that would drown Hetch Hetchy Valley - a place he considered the equal of Yosemite itself. The naturalist had fought for years to prevent San Francisco from flooding this glacier-carved sanctuary inside Yosemite National Park, but Congress authorized the project anyway, reasoning that public land should serve public benefit. Today, O'Shaughnessy Dam provides water to over two million people, and that water is so pure it needs no filtration. Meanwhile, the Sierra Club continues to advocate for removing the dam and restoring the valley Muir called a 'mountain temple.'

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Image: User:Inklein | CC BY-SA 3.0

O'Shaughnessy Dam: Fire and Water

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit tosh chiang, CC BY 2.0. San Francisco had coveted the Tuolumne River since the 1890s, when the city was already outgrowing its meager water supply of local springs and streams. But the Hetch Hetchy Valley lay within Yosemite National Park, protected land where utility development seemed unthinkable. The...

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Image: tosh chiang | CC BY 2.0

O'Shaughnessy Dam: Muir's Last Battle

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit Jennifer Williams from SOUTHERN PINES, USA, CC BY-SA 2.0. John Muir and the Sierra Club mounted fierce opposition to flooding Hetch Hetchy. The U.S. Army Corps of Engineers reported in 1913 that the Mokelumne River offered 'a better and cheaper source than Hetch Hetchy,' but San Francisco had become, in the words of historians, 'obsesse...

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Image: Jennifer Williams from SOUTHERN PINES, USA | CC BY-SA 2.0

O'Shaughnessy Dam: Sixty-Eight Lives

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit Matt Frederick at Flickr, CC BY 2.0. Construction claimed 67 men and one woman. Before the dam could rise, workers built a railroad through treacherous terrain, using Shay locomotives to negotiate winding curves and 4 percent grades. They constructed a smaller dam at Lake Eleanor first, providing electricity to powe...

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Image: Matt Frederick at Flickr | CC BY 2.0

O'Shaughnessy Dam: Crystal Clear

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit NVE from Norway, CC BY-SA 2.0. The Hetch Hetchy watershed produces some of the cleanest municipal water in America. Shallow soils over solid granite bedrock filter snowmelt naturally, and stringent protections - no swimming, no boating, though fishing is permitted - maintain water quality. San Francisco tap wa...

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Image: NVE from Norway | CC BY-SA 2.0

O'Shaughnessy Dam: The Debate Continues

Fri, 23 Jan 2026 00:00:00 GMT

Photo credit Jennifer Williams from SOUTHERN PINES, USA, CC BY-SA 2.0. The Sierra Club still lobbies for Hetch Hetchy's restoration, arguing that San Francisco could tap alternative sources like its unused allocation from Lake Don Pedro, the largest reservoir on the Tuolumne. A 2006 UC Davis study found that dam removal, combined with other infrastr...

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Image: Jennifer Williams from SOUTHERN PINES, USA | CC BY-SA 2.0