Upper Geyser Basin, Black Sand Basin
Black Sand Basin is a small part of the massive Upper Geyser Basin. To reach it, drive 0.4 miles north of the Old Faithful Interhchange, or 15.7 miles south of Madison Junction on the Old Faithful to Madison section of the Grand Loop Road. It gets its name from sands derived from volcanic glass, otherwise known as obsidian. Rather than being a loop like most thermal area trails, Black Sand is set up as a few short spurs.
Cliff Geyser is perched right on the edge of Iron Spring Creek. Large eruptions are uncommon, but the water frequently splashes over the edge of the cone.
Emerald Pool is a large hot spring with striking rings of color.
Green Spring is a large, shallow, very hot spring. It has had minor eruptions over the years, but is mostly quiet.
Opalescent Pool is a beautiful pool, but it is not a hot spring, at least not any more. All of its water is runoff from Spouter Geyser. The cooler temperatures allow the brownish bacteria to grow.
Rainbow Pool is a large multicolored pool about 100 feet across. It is usually a calm spring. In May 1996 it had eruptions as much as 100 feet tall, but nothing like it has occurred since.
Spouter Geyser is a small light blue pool that perpetually erupts one to three feet high.
Sunset Lake is an enormous hot spring. It has historically had eruptions of up to 35 feet high. It generates such a massive steam cloud that it is often difficult to observe any potential activity.