Steve Cotler

Steve Cotler

Subway Cave

Some 20,000 years ago, a volcanic eruption sent gouts of lava into what is now Northern California’s Hat Creek Valley. This molten rock, like any liquid, flowed downhill, gravity pulling it into the lowest channels. These rivers moved slowly, the sides and top cooling as they touched ground and air. A hardened skin slowly formed around the molten flow, creating a rock tube through which the still-liquid lava continued its downward movement. If the gradient was steep enough—and the viscosity low enough—the “skin” stayed put as the liquid rock evacuated the tube, leaving a hollow channel.

Lavacicles hanging from the lava tube's ceiling

Shasta County’s Subway Cave, just north of Old Station, CA, is one such lava tube. About 1,400 feet long, the cave was hidden from view for millennia until the roof collapsed in two places. Native Americans knew of it, but researchers believe they left it unused, believing it inhabited by malevolent spirits.

Pitch dark inside, one enters by concrete steps at either end. The floor is flat and knobbly—just as one would expect a hardened flow of rock to be—and the roof is high enough for one to walk upright. A flashlight is necessary.

Interesting geology. And not overrun by tourists.

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