West Thumb Geyser Basin Trail

This easy boardwalk circuit circles West Thumb Geyser Basin at Yellowstone Lake's edge. The full loop is listed at 0.6 mile (1 km), though mapped descriptions of the outer circuit reach about 0.65–0.7 mile. A center cut-through makes it shorter. Allow 30–60 minutes if you stop to look at the pools; this is a compact geothermal walk, not a backcountry hike.

Start at the West Thumb Geyser Basin parking area and follow the boardwalk out through the thermal basin. The longer circuit passes Abyss Pool and Black Pool, then descends toward the lake. Along the shore, look for Big Cone, Fishing Cone and Lakeshore Geyser; the return bends inland by Seismograph Pool and the Thumb Paint Pots. The inner loop and center crossing give you shorter options.

The lake-facing boardwalk is the best place to pause for the setting: frame Abyss Pool with Yellowstone Lake and the Absaroka Range beyond. The east-facing pools can show richer color in afternoon light, though steam and weather change the view.

Abyss Pool is about 53 feet deep, and its turquoise-green color shifts with light, water chemistry and biology. Black Pool earned its name when cooler water supported dark-colored microbes; after it warmed in the early 1990s, the pool turned blue-green. These are good places to slow down and notice how different the basin's pools look from one another.

Big Cone, Fishing Cone and Lakeshore Geyser sit close to Yellowstone Lake. Their vents can be partly covered as lake levels rise and fall, so the cones do not always look the same from the boardwalk. Fishing Cone recalls a 19th-century practice of lowering freshly caught fish into its hot vent to cook; visitors stopped after the practice damaged the cone. A geyser erupts when steam pressure builds below a narrow part of its underground plumbing and forces water upward.

On the inland return, the boardwalk passes Seismograph Pool and the Thumb Paint Pots. The paint pots are gray, acidic mud; sulfuric acid formed from hydrogen sulfide alters rock into the fine clay. How much the pots bubble or spit mud varies, so a quiet pool is still part of the same hydrothermal system.

The trail begins by the West Thumb basin parking area, near the information kiosk. The trailhead has designated accessible parking and a vault or composting toilet. No separate trail fee or reservation is listed, but the park entrance fee may apply. Pets are not allowed on the boardwalk. Stay on the boardwalk and designated paths: hydrothermal water can severely burn you.