Northern California - Mount Lassen, Pit River, and Modoc Plateau
			As molten lava in a volcanic eruption flows downhill it tends to harden first around the outside of the flow. If the end of the flow breaks open, lava from the still-molten center may all run out, leaving a long tubular cave. The Modoc area is particularly rich in lava tube caves, including Lava Beds National Monument.
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