Qualla: Clear Lake: California's Ancient Inland Sea

Clear Lake: California's Ancient Inland Sea: Introduction

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit Kim Joar Bekkelund, CC BY 2.0. The name is a lie, and everyone who lives here knows it. Clear Lake has not been clear for decades. Algal blooms cloud the water green each summer, mercury from an abandoned mine taints the fish, and the lake that Rachel Carson wrote about in Silent Spring still carries the chemical legacy of a mid-century war against gnats. Yet this murky, complicated body of water is also the oldest natural lake in North America, nearly half a million years old, sitting in a basin where lakes have formed and reformed for 2.5 million years. At 68 square miles, it is the largest natural freshwater lake entirely within California, and it remains, despite everything done to it, a place of extraordinary ecological richness.

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Image: Kim Joar Bekkelund | CC BY 2.0

Clear Lake: California's Ancient Inland Sea: A Basin That Refuses to Die

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit Bill Larkins, CC BY-SA 2.0. Most lakes are geologically temporary. They fill with sediment, drain through shifting outlets, and vanish within tens of thousands of years. Clear Lake has persisted for roughly 480,000 years because of a geological trick: the massive block of rock beneath it tilts slowly northw...

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Image: Bill Larkins | CC BY-SA 2.0

Clear Lake: California's Ancient Inland Sea: Eleven Thousand Years of Habitation

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit Natoma Gardner, CC0. Archaeological evidence places human occupation of the Clear Lake basin at least 11,000 years into the past. The Pomo, Lake Miwok, and Wappo peoples built their lives around the lake's abundance. The Pomo called it Hok-has-ha. They wove tule grass into cooking baskets, fishing ne...

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Image: Natoma Gardner | CC0

Clear Lake: California's Ancient Inland Sea: Silent Spring's Proving Ground

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit U.S. Army Corps of Engineers Sacramento District, Public domain. In the 1940s, Clear Lake's phantom midges swarmed so thickly that lakeside resorts complained about losing business. The gnats did not bite, but they arrived in clouds. In 1949, authorities applied DDD, a pesticide related to DDT, directly to the lake. The gnats died. So did the ...

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Image: U.S. Army Corps of Engineers Sacramento District | Public domain

Clear Lake: California's Ancient Inland Sea: Water Wars on the Rumsey Gauge

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit Arnaudh, CC BY 3.0. In 1872, a cattle drive captain named DeWitt Clinton Rumsey installed a gauge in Lakeport to measure water level. He defined zero as the point where water stopped flowing over a rocky ledge in Cache Creek called the Grigsby Riffle. That gauge, now automated, still operates. Yolo ...

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Image: Arnaudh | CC BY 3.0

Clear Lake: California's Ancient Inland Sea: A Lake Between Ruin and Restoration

Thu, 02 Apr 2026 00:00:00 GMT

Photo credit Public domain. Clear Lake today is a place of contradictions. Over 100 miles of shoreline draw 15,000 boaters a year, and the lake hosts the oldest and largest seaplane splash-in in the western United States. Tule elk, hunted to local extinction a century ago, have been reintroduced and are gro...

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Image: Public domain