The Bumpass Hell trail is the main route to the park's largest hydrothermal area — a 3-mile round trip from an 8,200-foot trailhead that descends into a steam-filled basin of boiling pools, mudpots, and fumaroles covering 16 acres. It's the most popular trail in the park, and for good reason: there's nothing else in California quite like walking a boardwalk above an active hydrothermal system.
Overview
Bumpass Hell sits in a collapsed caldera remnant on the southern flank of Lassen Peak, where superheated water from deep underground emerges as boiling mud, acidic pools, and hissing steam vents. The trail was named for Kendall Vanhook Bumpass, who discovered the area in the 1860s and lost a leg to a mud pool — a fact the NPS still includes in its signage as a useful warning.
What to Expect
The trail climbs gradually for the first mile, then drops about 300 feet into the hydrothermal basin over the final half mile. A boardwalk loops through the basin and keeps you on solid ground over what is, in places, a very thin crust above boiling water. Stay on the boardwalk. The pools are acidic enough to cause severe burns on contact. Trail surface is packed gravel throughout.
Tips & Logistics
The trail typically opens in late July after snow clears — dates vary by year, so check the park website before planning around it. The trailhead is on the main Lassen Volcanic Highway, well-signed. Crowds are heaviest from mid-morning to early afternoon; an early start reduces congestion and sun exposure. No permit required. No water on trail. Dogs are not allowed. Allow 2 hours for the full round trip.