The lava tube was named after the Mount St. Helens Silvertip Mountaineers, a group that originally called themselves the 'Apes'.
It is the third-longest lava tube in North America.
The cave was formed by the fluid basaltic lava flows of the 1,900-year-old Cave Basalt eruption.
Unlike many other caves, Ape Cave does not contain stalactites or stalagmites because the lava flow did not drip from the ceiling as it solidified.
The ceiling height reaches up to 30 feet in some sections, while the width extends to 50 feet.
A unique type of cave slime, or 'cave bacteria,' covers some surfaces, appearing as a thick, white mat.
The cave floor is largely composed of hardened lava flows known as pahoehoe, which can be smooth or jagged.
Ape Cave is a two-mile-long lava tube located on the southern flank of Mount St. Helens in Washington State. Formed approximately 1,900 years ago, it remains one of the longest continuous lava tubes in the continental United States. The site features two distinct routes: the lower cave, which is relatively easy and family-friendly, and the upper cave, which requires scrambling over large boulder piles. A consistent subterranean temperature of 42 degrees Fahrenheit persists year-round regardless of surface weather. The environment is entirely dark, necessitating high-powered artificial light sources for safe navigation. Management is handled by the U.S. Forest Service within the Gifford Pinchot National Forest. The site is a fragile ecosystem serving as a habitat for troglobitic species including specialized fungi and insects.
The main entrance at the base of the staircase, where light filters into the cave mouth, creating a high-contrast transition zone.
Bring at least two reliable light sources per person, as cell phones are insufficient and batteries drain faster in the cold.
Wear sturdy hiking boots with good ankle support to navigate the uneven, rocky terrain.
Layer your clothing; the constant 42-degree temperature feels freezing after walking from a hot summer day.
Attempting the upper cave without proper physical conditioning or climbing gear for the steep boulder obstacles.
The site is typically closed during the winter and early spring months due to snow-blocked access roads.
Do not touch the cave walls to protect the fragile microbial colonies; stay on the marked path; pack out all trash.
