Bumpass Hell

Bumpass Hell is a 16-acre basin of bubbling pools, mud pots and fumaroles on the high volcanic slopes of Lassen Volcanic National Park. Its boardwalks take you among the steam, mineral colors and sulfur smell. I'd make time for it if you're up for a 3-mile hike: this is the park's largest hydrothermal area, and you get more than a roadside peek.

Allow 90 minutes to two hours for the round trip. The trailhead is about 7 miles north of the Southwest Entrance. Parking often fills from mid-morning through early afternoon, especially on weekends, so go early or later in the day. Vault toilets are at the trailhead; there are none along the trail or in the basin. No food or potable water is listed for this stop, so bring enough water and a snack. Much of the route is exposed. Pets aren't allowed on park trails, even in carriers; service animals are allowed.

The first mile climbs gradually. At about half a mile, a broad overlook opens onto five remnant peaks of Brokeoff Volcano. Near mile one, another overlook looks down into Bumpass Hell. From there the trail drops about 300 feet to the basin, with a steeper, rockier stretch at the end. You'll climb that same ground on the way back out. The first mile is mostly firm and wide, but the final half-mile is narrow and uneven, so the whole route isn't accessible.

The basin is full of steam vents, bubbling pools and mud pots. Sulfur gives it a strong rotten-egg smell, and the pools and vents can rumble and hiss as well as steam. The scene changes through the year: spring snowmelt cools some features and makes the mud more fluid, while dry late summers can leave them hotter and drier.

Big Boiler is the park's largest fumarole. Measurements found its steam as hot as 322°F (161°C). Bumpass Hell is the main upflow and steam-discharge area of Lassen's hydrothermal system: rain and snowmelt seep underground, heat from hot rock turns water to steam, and gases rise through fractures. The pools are typically acidic and aren't safe to bathe in.

The basin is named for Kendall Vanhook Bumpass, who found it in the 1860s. A thin mudpot crust gave way under him and badly scalded his leg. It is a vivid reminder that the pale ground around a pool can be a fragile lid over boiling mud or water.

The wide view from the half-mile overlook takes in five peaks left from ancestral Brokeoff Volcano, also called Mount Tehama. From the basin overlook, frame the boardwalk against the pale mineral slopes; the close-up pools, steam and altered rock are the payoff once you walk down. The best basin views require the full hike from the parking area.

Keep to the marked trail and boardwalk. The crust beside the pools can hide acidic boiling water or mud, and stepping off the path is both dangerous and prohibited. Snow can keep the trail closed into early summer; opening and closing dates shift with snowpack, so check current trail conditions before you go.