Biscuit Basin

Biscuit Basin is a compact group of hot springs and small geysers in Yellowstone’s Upper Geyser Basin. Its easy 0.6-mile (1-kilometer) lollipop loop follows a boardwalk past several named features, making this a good short stop when you want a close look at the basin’s color and activity.

The loop passes Sapphire Pool, Avoca Spring and Jewel Geyser. Jewel typically erupts every 7 to 10 minutes, though geysers do not keep a guaranteed schedule. Mustard Spring adds a bright color contrast to Sapphire’s blue water.

Biscuit Basin is also the starting point for the Mystic Falls Trail. The 2.4-mile round trip crosses mixed conifer forest to a 70-foot drop on the Little Firehole River. Treat this as a separate hike, not an extension of the short basin loop.

Sapphire Pool’s saturated blue water and pale mineral rim make the basin’s clearest photo subject. Keep both in the frame from the boardwalk; steam can drift across the surface and change how much of the pool shows.

Geyserite deposits once formed rounded, biscuit-like shapes around Sapphire Pool. An eruption associated with the 1959 Hebgen Lake earthquake blew them away, but the name remained. NPS records Sapphire Pool’s last eruption in 1991.

Black Diamond Pool has exploded more than once. USGS infers an early event between 1902 and 1912 from the aftermath, then documents further activity in 1918, 1925, 1934 and 1953. Explosive activity resumed in 2006, and the July 2024 event was the pool’s largest recorded activity.

Older accounts use names such as Black Pearl, Black Opal, Wall Pool and Black Diamond in ways that do not always match later maps. Some early observers used “Black Pearl” for multiple pools, while “Black Diamond” became the common name for the larger Wall Pool feature much later. That naming history can make older photos and descriptions hard to match to today’s labels.