After starting on the nearby quarter mile Two Forests hike, Lava Canyon is a relatively short dayhike across from the trailhead to Ape Canyon. There is a short, medium, and long version, each one getting more difficult and exposed. The eruption on Mt Saint Helens in 1980 washed away the covering forest to expose the carved riverbed from much earlier.
The 5.5 mile hike up Ape Canyon actually stays on a ridge and in the forest, which was nice because it was very hot and sunny. I found a stand of trees right next to where the trail meets the Loowit Trail to camp at.
From camp the first evening I hiked up Pumice Butte for views of the peak and the plains. The next day I hiked to Windy Pass and out to the rim above Smith Creek.