From Washington To You
Visitors with headlamps on an interpretive tour inside Ape Cave lava tube.
Photograph by the U.S. Forest Service, Pacific Northwest Region, Gifford Pinchot National Forest. Public domain.

From Washington to you

Ape Cave

Ape Cave · Skamania County · Cave Basalt about 1,895 years ago

A pahoehoe lava tube on the southwest flank of Mount St. Helens is the third longest in North America.

Ape Cave is one of numerous lava tubes formed in the Cave Basalt about 1,895 years ago. The basalt lava flows have the form of pahoehoe flows that originated on the southwest flank of Mount St. Helens and flowed down the surface of older pyroclastic-flow deposits.

USGS calls the Ape Cave lava tube the third longest lava tube in North America — about 4 km or 2.5 mi. It is open year round. Guided cave walks are offered daily during the summer visitor season. In winter months, a Sno-Park Pass is required to enter the area.

The cave is inside Mount St. Helens National Volcanic Monument, established in 1982 to designate 445 km² (110,000 acres) around the volcano for research, recreation, and education. The monument is within Gifford Pinchot National Forest and is managed by the USDA Forest Service.

  • Geography & Geology
  • Science / Strange Washington

Sources (1)

Last reviewed: September 20, 2026

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