Ape Cave Geologic Site is on FR 8303, 1 mi. w. of FR 83. Thought to be the third longest lava tube in North America, the 13,042-foot tunnel was found within a massive lava flow that oozed from the volcano almost 2,000 years ago. Flowing downhill, the stream of lava cooled and formed a hard crust. In time the lava drained and left an intricate, winding lava cave behind. The cave was discovered in 1947 but not explored until the early 1950s by a local Boy Scout troop. The scouts named the cave in honor of their sponsor, the St. Helens Apes.
Visitors should have a minimum of three light sources, extra batteries, sturdy shoes and a jacket; the temperature is a constant 42 degrees Fahrenheit. Rental propane lanterns are available at Ape Headquarters.