Bumpass Hell

Bumpass Hell is the showpiece hydrothermal area of Lassen Volcanic National Park, a 16-acre basin of hot springs, steaming fumaroles and boiling mudpots set inside the eroded caldera of an ancient volcano. Water here reaches about 198°F (92°C), near the boiling point at this altitude, and the ground around it has been altered into bright clays streaked with sulfur, pyrite and iron oxides. The springs change through the year: clear in early summer when water is plentiful, then cloudier, then spattering mud, and finally just steam as the season dries out.

You reach the basin on a 2.8-mile round-trip trail the Park Service rates as moderate, with one steep stretch where trekking poles help; it is sun-exposed and high, so carry water. Parking at the trailhead is limited and the trail is busy, so arrive early. Inside the basin, stay on the boardwalk and marked path, since the crust over the hot water is thin and the water will scald.

This is strictly look, don't soak. Expect a park entrance fee rather than a trail fee. The trail opens only after the heavy snowpack melts, often well into summer, so check the park's opening history before planning.

The downside: the season is short, and on summer weekends you share the boardwalk with crowds.