Black Sand Basin, Yellowstone National Park, Wyoming

This photo shows part of a low, rounded slope seen at the Black Sand Basin (an isolated group of the Upper Geyser Basin) in Yellowstone National Park. Hot water from the very nearby Cliff Guyser flows down this slope into Iron Creek.

"Black Sand Basin is only about 1/2 mile from Old Faithful Geyser. It was named for the course black obsidian sand that surrounds the thermal features there."

"The vivid colors are the result of pigmented bacteria in the microbial mats that grow around the edges of the mineral-rich water. The bacteria produce colors ranging from green to red; the amount of color in the microbial mats depends on the ratio of chlorophyll to carotenoids and on the temperature of the water which favors one bacterium over another. In the summer, the mats tend to be orange and red." From WIkipedia.