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Natural Bridges (Gifford Pinchot)

From Oregon Hikers Field Guide

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The first natural bridge (bobcat)


Two natural bridges span a collapsed lava tube near Peterson Prairie. The tube itself, known as the Big Trench, is almost a mile in length and varies between 20 and 75 feet deep. Like the nearby Guler Ice Cave and the scores of other lava tubes in the area, the formation was produced during lava flows 12,000 – 18,000 years ago that issued from the crater now occupied by Lake Wapiki in Indian Heaven. Lava tube collapses are not usually the result of thousands of years of weathering and erosion; rather, they occurred during the formation of the tube itself as molten lava passed through, leaving a cavern, and the solidifying "ceiling" fell under its own weight.

You can walk on both of the bridges and spend more time exploring the rim of the Big Trench. You can also descend to the uneven and rubbly trench floor to enter cave systems in sections of the tube that did not collapse. In two or three places, there are side tubes branching off.

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