Black Sand Basin - Obsidian Sand and Emerald Water

Photo: NetwonsBucket, CC BY-SA 4.0 (cropped)

A stop on Yellowstone Geyser Country, a free self-guided tour.

Look down at the ground along the boardwalk and you'll see why this small basin got its name: the dark grains are bits of obsidian, natural volcanic glass worn down into sand.

The boardwalk loop is short, but it packs in color. Emerald Pool owes its green to a simple mix: yellow microbes lining the bottom blend with the blue of deep, clear water. Sunset Lake, a large and steamy pool, is actually a geyser, though its eruptions are rare and easy to miss in the haze. Cliff Geyser, perched on the bank of Iron Spring Creek, can splash up to about 40 feet when it's active.

This is a good place to talk with kids about why the water is so colorful and so dangerous. These pools are near boiling, and the ground around them can be a thin crust over scalding water. Stay on the boardwalk, never touch the water, and remember that pets aren't allowed on thermal boardwalks.

Getting here: Walk back to your car at Old Faithful and drive north on the Grand Loop Road about a mile; the Black Sand Basin turnoff is on the left.

Did you know?: Some of the rhyolite stone used to build the Old Faithful Inn came from the Black Sand Basin area.

Photo op: Shoot Emerald Pool from the boardwalk with the sun high behind you for the richest green; on cool mornings, the steam drifting off Sunset Lake makes moody backlit shots.

Nearby: No food or water here; the nearest full services are back at Old Faithful, about a mile away.

More on Wikipedia: Black Sand Basin Hot Springs

Black Sand Basin - Obsidian Sand and Emerald Water

Stops on this tour