Gannett Peak Name
       7 ½’ quadrangle: Gannett Peak, WY
       Fremont and Sublette Counties
       On the divide between Bridger-Teton National Forest (Bridger Wilderness) and
       Shoshone National Forest (Fitzpatrick Wilderness)
      Wind River Range, Rocky Mountains

Metamorphic (metamorphosed igneous)
13,804 ft (4,207m)

Wind River Range from the south, viewed across U-shaped glacial valley and Fremont Creek.
Peaks on the skyline are, right to left: Jackson, Fremont, Sacajawea (sharp, with steep drop
to left), Helen, and Gannett (behind peak in shadow). (1997)

Bedrock: Unnamed migmatite

Archean

Foliated quartz-plagioclase-biotite gneiss, massive granite, hornblende gneiss with melasomes of amphibolite, biotite schist, biotite gneiss and lesser metadiabase and banded iron formation. Two generations of migmatite are present, plus younger pegmatite and aplite dikes. The Wind River Range rose along faults during the Laramide Orogeny in the Late Cretaceous.

Surficial Geology: Pleistocene glaciers carved cirques, arêtes, horns and U-shaped valleys to create a landscape that some say rivals that of Yosemite. Remnant glaciers remain: Gannett Glacier to the north, Minor Glacier to the west, Gooseneck Glacier leading east just south of the summit (the main ascent route) and Dinwoody Glacier farther south toward Dinwoody Pass.

Soil Series: Snowfield covering bedrock

Selected References:

• Worl, R.G., M.E. Koesterer and T.P. Hulsebosch, 1986, Geologic map of the Bridger Wilderness and the Green-Sweetwater Roadless Area, Sublette and Fremont Counties, Wyoming: U.S. Geological Survey Map MF-1636-B.

Other suggested sources of information:

• Glossary: http://www2.nature.nps.gov/geology/usgsnps/misc/glossaryAtoC.html
• Time scale: http://www.ucmp.berkeley.edu/help/timeform.html
• Wyoming Geological Survey: http://www.wsgs.uwyo.edu/mapping/default.aspx