Monument Geyser Basin

Monument Geyser Basin is a compact thermal area on a hillside above Beryl Spring, west of Gibbon Canyon. The pale basin runs about 300 by 100 metres, dotted with steam vents, boiling pools, mud pots and sulfur deposits. Plan this as a hike to an unusual thermal landscape, not as a drive-up stop.

The trail from the Grand Loop Road pullout is steep and 2.4 miles round trip. It follows the Gibbon River at first, then turns uphill; the last half-mile climbs especially steeply. Visitors often single out the odd basin and views toward the river valley as the payoff, but the climb is the main effort.

About half a dozen sinter deposits form chimney-like spires on the pale slope, with some rising to around 3 metres. The sinter sits among small hot springs and steam vents that appear as boiling pools, frying pans, mud pots and fumaroles. The unusual shapes give the basin its name.

The basin sits on thick Lava Creek Tuff cut by faults. Acidic, steam-dominated fluids alter the rock, dissolving silica that later redeposits as sinter and builds the pale ground and spires. The spires follow the fault pattern; their shape suggests a glacially dammed pond may have been present while they formed. Their chimney-like forms resemble the silica structures that can grow around deep-sea hydrothermal vents.

Off-trail travel is prohibited in thermal areas, and pets are not allowed on the trail. A roadside pullout and information kiosk are at the trailhead. If the established route gives you a clear view, frame a pale spire with a steaming vent against the darker tree line; don't step onto the thermal ground for a closer photo.