Abstract The Yellowstone Geoecosystem ( Smith and Siegel, 2000 ; Morgan, 2007 ) comprises an amazing diversity of geologic features that control the character and distribution of geothermal features and soils of this landscape. The underlying bedrock geology of Yellowstone National Park (YNP) includes: Precambrian basement along the northern margin of the Park, with both low-grade metasedimentary rocks (biotite-andalusite-staurolite schists, quartzites and banded iron formations) and late Archean granitoid rocks. Phanerozoic sedimentary rocks in the northwestern corner of the Park in the southern Gallatin Range, that includes notably the Mississippian Madison Limestone near Mammoth Hot Springs, and Cretaceous shales and sandstones of the Kootenai, Eagle, Frontier and Harebell formations, south of Gardiner. The voluminous Eocene Absaroka Volcanics dominantly consisting of andesitic flows, tuffs, volcaniclastic rocks and hypabyssal intrusions. The iconic caldera-forming eruptive rocks of the Tertiary Huckleberry Ridge Tuff (2.1 Ma), Mesa Falls Tuff (1.2 Ma), and Lava Creek Tuff (0.61 Ma) of dominantly rhyolitic composition, and the post-caldera rhyolites (Christansen, 2001). The surficial geology of YNP ( Good and Pierce, 1996 ) additionally involves complex interactions of glacial geology ( Pierce, 1979 ) and active tectonics ( Pierce et al., 2007 ; Smith references). Tertiary volcanism and associated hydrothermal activity are directly related to the elevated hot spot that formed the regional Snake River Plain-Yellowstone system ( Smith and Siegel, 2000 ). Yellowstone contains the greatest number and diversity of geothermal systems on the planet, yielding an extensive array of extreme high-temperature environments, many of which are colonized by microorganisms that play either