Big Basin is a large circular depression. It is about one mile in diameter and about 100 feet deep. The walls of the basin are nearly vertical. Scattered across the floor of Big Basin are a number of small ephemeral ponds that catch and temporarily hold the water that flows into the basin.
U.S. Highway 283 bisects Big Basin, with approximately two-thirds of the basin lying east of the road and within the confines of the preserve. The remaining western third of the basin is privately owned.
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