Beneath the waters of a California reservoir lies a valley once compared to Yosemite.

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: Hetch Hetchy Reservoir provides water to millions in the San Francisco Bay Area, yet it hides a submerged history. While visitors now admire the granite cliffs and waterfalls from the O’Shaughnessy Dam, the landscape remains a subject of debate regarding its transformation from a glacial valley into a vital water source.

The Hetch Hetchy Reservoir is a massive engineering feat, stretching eight miles in length with a maximum depth of 306 feet. At its heart, the O’Shaughnessy Dam stands 312 feet above the streambed, spanning 910 feet in a gentle arch. This structure allows the reservoir to hold approximately 117 billion gallons of water, which is released downstream to support fish, wildlife, and recreation along the Tuolumne River throughout the year.

Before the dam was completed, the valley was renowned for its natural beauty, featuring towering granite formations like the Hetch Hetchy Dome on the north side and Kolana Rock on the south. Today, these landmarks frame a landscape that serves as a gateway to the Yosemite wilderness. Hikers can access numerous trails from the dam, leading into areas such as Pate Valley, Jack Main Canyon, and Poopenaut Valley, where the terrain ranges from easy walks to strenuous backpacking routes.

The area remains a biodiversity hotspot, hosting a variety of flora and fauna. Hikers may encounter black bears, mountain lions, and mule deer, while birdwatchers can spot golden eagles, bald eagles, and peregrine falcons, which use Kolana Rock as an active breeding site. The region is also home to diverse plant life, including California poppies, lupines, and big leaf maples, which thrive alongside the reservoir’s dramatic waterfalls, such as Tueeulala and Wapama Falls, which drop over 1,000 feet from the surrounding cliffs.

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