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Geology of National Parks, 3D and Photographic Tours

Pinnacles National Monument
Bear Gulch Cave (downstream from the dam and reservoir) owes its origin to rapid flood events and debris flows which episodically carve the canyon. The cave consists of passages between large boulders of volcanic tuff. The great blocks and boulders of volcanic rock that cover the creek bed (creating the cave) may have collapsed from the slopes above during rockfalls and landslides, possibly associated with major earthquakes in the past (Rogers and others, 2003).
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