Yellowstone National Park
Upper Geyser Basin

Grand Geyser Basin is the historic name for Upper Geyser Basin thermal springs area within the greater Firehole River drainage basin. This basin is host to Grand and Giant geysers.

The odd-shaped features in the bottom of the hot pool are great colonies of thermophilic microbial mats growing on siliceous sinter deposits. The organic growth probably assists the precipitation and trapping of sediments.

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Last modified: 10/17/2009