Black Sand Basin is one of the shortest walks in Yellowstone National Park—but that doesn’t mean it’s short on sights or spectacular things to see. Rather, this volcanically heated, bubbling basin is a packed with geysers and pools, from the periwinkle colored Opalescent Pool, to the Spouter Geyser which consistently erupts for up to 10 hours at a time. At Emerald Pool, where the water temperature is slightly lower than neighboring Rainbow Pool, the water casts a deep green hue of molten emeralds, whereas Rainbow Pool is slightly warmer and tinged with yellow and orange. Occasionally, depending upon eruptions, the Cliff Geyser will come to life and send water 40 feet high, although unlike Old Faithful just one mile south, the interval is irregular enough to the point you should consider yourself lucky if you see it erupt. As for how it acquired its name, Black Sand Basin is named for obsidian that’s been crushed down into the earth.