Black Sand Basin Loop

Black Sand Basin is a compact hydrothermal area located one mile from Old Faithful and accessible via a short boardwalk loop that circles several of Yellowstone's most vivid and photogenic hot springs. The basin takes its name from the black obsidian sand—volcanic glass fragments—that lines several of the spring pools and the adjacent Firehole River bank, contrasting dramatically with the aquamarine and emerald green of the thermal pools. Emerald Pool is the centerpiece, its deep green color produced by the combination of yellow sulfur deposits on the pool floor and the brilliant blue of the hot water above—a color that shifts dramatically with cloud cover and time of day. Rainbow Pool adjacent to it displays the full spectrum of thermophilic microbial mat colors, from deep red and orange through yellow and pale green, arrayed in concentric rings outward from the scalding center. Handkerchief Pool, once a popular attraction where visitors would drop handkerchiefs and watch them disappear and reappear after circulating through underground connections, has permanently subsided. The Firehole River bordering the basin is fed by dozens of thermal inputs throughout the Upper Geyser Basin, making it one of the warmest rivers in the park despite its swift current. The loop can be easily combined with a visit to Old Faithful and the Upper Geyser Basin boardwalks into a comprehensive half-day hydrothermal tour.