Black Sand Basin is an isolated group of the Upper Geyser Basin located along the Firehole River about one mile from Old Faithful in Yellowstone National Park. The name derived from the black fragments of obsidian sand that covers the basin of small geysers and colorful hot springs. Sunset Lake is a shallow thermal pool with a soft sinter bottom with yellow and orange bacteria and algae edges. It empties into Iron Creek and overflows into the Rainbow Pool which creates a microbial mat between the two thermal pools. | 
