Viciously jagged black rock covers most of this small national monument. These are lava flows from recent geologic times, and new eruptions could conceivably occur. The whole area is riddled with lava tube caves, some with developed access, others completely wild and many probably still undiscovered. There are also other volcanic features, such as splatter cones, cinder cones, and eruption craters
Skull Cave, named for bighorn sheep skulls found deep inside, is one of the largest diameter lave tubes. Its lowest level is floored with year-around ice.
 | The incredibly rough Devils Homestead Lave Flow, riddled with lava tube caves (July 20, 2011) Standard Size or Large Size | |
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 | The Geography field class 2004 enjoys the sunset from Fleeners Chimneys, a splatter cone (September 18, 2004) Standard Size or Large Size | |
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 | The Fleener Chimneys are a volcanic eruptive feature known as splatter cones (July 21, 2011) Standard Size or Large Size | |
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 | Looking down the throat of one of the Fleener Chimneys, a source of the Devils Homestead Lave Flow (July 21, 2011) Standard Size or Large Size | |
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 | The Bunchgrass trail viewpoint looks north to Schonchin Butte and Tule Lake (July 20, 2011) Standard Size or Large Size | |
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 | This shallow section of Skull Cave has collapsed, offering entry to the cave in both directions (July 21, 2011) Standard Size or Large Size | |
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 | Stone steps and a paved trail lead down into Skull Cave (July 21, 2011) Standard Size or Large Size | |
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 | Skull Cave drops slowly at first, then turns a corner and plunges down into darkness (July 21, 2011) Standard Size or Large Size | |
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 | A paved trail and aluminum ladders make huge Skull Cave easy to explore (July 21, 2011) Standard Size or Large Size | |
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