Ape Cave

Easy (Lower cave)

2 miles round trip

200 feet elevation gain

Open all year

Moderate (Upper cave)

3-mile loop

400 feet elevation gain

Easy (Trail of Two Forests)

0.2-mile loop

No elevation gain

Longest lava tube in the western hemisphere, Ape Cave features a 0.8-mile lower section that’s easy to hike and a rugged, 1.4-mile upper section that’s fun for adventurers. The lower section, with a smooth, sandy floor, leads to The Meatball, a lava boulder wedged halfway to the cave’s 30-foot ceiling. The rugged upper section of the cave offers a skylight and two frozen lava “waterfalls,” but a jumble of rocks on the cave floor makes walking difficult.

Bring at least one lantern or flashlight for each person and be sure to dress warmly. Even on hot summer days the drafty cave remains a chilly 42° F. Pets, smoking, food, and beverages are banned in the cave. If you don’t have a Northwest Forest parking pass you can buy one at the trailhead. There is no extra fee per person, but if you want to rent a lantern expect to pay $5. Although the cave is open all year, the entrance road is gated closed from December 1 to April 15, adding a mile to your hike each way.

Ape Cave formed 1900 years ago when Mt. St. Helens erupted a runny kind of basalt lava known as pahoehoe. As the flow’s crust hardened, the liquid lava underneath drained out along the course of a buried stream gully, leaving a 11,334-foot-long tube. In places the tube was so tall it pinched into two separate levels, one above the other. Watch along the walls for stripes, the “high-water marks” left by flowing lava. Also look for solidified puddles of the lava river on the cave floor, often with ripple patterns like cake batter poured in a pan.

As the lava ebbed, superheated gases blasted through the tube, remelting the walls’ surface and leaving tiny, fragile stalactites known as “lava drips.” Since then, earthquakes have shaken loose portions of the upper cave’s ceiling. An eruption of Mt. St. Helens 450 years ago loosed a mudflow that spilled into the cave’s main entrance and paved the lower cave with sand. Remarkably, the 1980 eruption had almost no effect here.

Discovered in 1946, Ape Cave was named for the Mt. St. Helens Apes, a group of Boy Scout cavers who took their tongue-in-cheek name from an alleged 1924 sighting of Sasquatch on the mountain’s east flank at an otherwise unrelated valley, Ape Canyon. To find the cave, drive Interstate …

This chapter taken from the book 100 Hikes/Travel Guide: Northwest Oregon & Southwest Washington.