Pinnacles National Park
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 spheroidally weathered boulders of volcanic tuff. The caves exist because the stream down cutting is proceeding faster than the rock can break down into sediments and soil. The great blocks and boulders of volcanic rock that cover the creek bed (creating the cavern) 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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Last modified: 10/21/2010