The Upper Fremont Glacier (43°07'N, 109°37'W) is located in the Wind River Range of Wyoming's Fitzpatrick Wilderness Area, 
and is named for Fremont Peak, one of the highest mountains in Wyoming, which borders the glacier to the West.

The Upper Fremont Glacier is of interest to researchers mainly because of its ability to preserve atmospheric records in the ice. 
The ice preserved the records due to its average altitude of 4,100 meters. The glacier, among the highest of all the glaciers 
in the Wind River Mountain Range, is about 2.2 kilometers in length and 1.3 kilometers in width at the widest point. 
The glacier has a near-level surface gradient, which results in a small surface velocity (movement) of about 3 meters per year. 
The high altitude of the glacier minimizes meltwater percolation and re-freezing. Thus, the isotopic integrity of the ice 
tends to be preserved.

David Naftz of the U.S. Geological Survey (USGS) took the first glacial measurements from this site in 1990-91. 
Also collected in 1991 was a continuous, 160-meter ice core that represented the entire depth of the glacier, 
from the surface down to the bedrock. The core was collected with a solar-powered, thermal drill, 
because the glacier is located in a designated wilderness area and the U.S. Forest Service desired the environment 
to be impacted as little as possible. Analysis of this ice core provided a tremendous amount of information, 
including the following:

    Identification in the ice of bomb-produced 36Cl, 129I, and tritium (Cecil and Vogt, 1997)
    Preservation in the ice of the end of the "Little Ice Age" (Naftz, 1996)
    Global linkage with the Quelccaya Ice Cap, Peru, South America (Naftz, 1996)
    Preservation in the ice of a warming trend in the environment that continues today (Naftz, 1996)

In September 1997, funding was obtained to resume studies of the Upper Fremont Glacier. Three weather stations 
were placed either on or near the Upper Fremont Glacier. Data was collected from these stations until July of 2001, 
when they were removed. In July - August 1998, an expedition returned to the glacier and collected two additional 
ice cores, one that started at the surface and went down 50 meters, and the second that spanned the distance 
from the surface to the bedrock.

The 1991 ice core from the Upper Fremont Glacier has been completely used up for various types of analyses. 
Some portions of the 1998 ice cores are still waiting to be processed and analyzed, but many sections have been 
analyzed for such things as tritium, 36Cl, delta 18O, and common ions.

References:

Schuster, P.F., D.P. Krabbenhoft, D.L. Naftz, L.D. Cecil, M.L. Olson, J.F. Dewild, D.D. Susong, J.R. Green, and M.L. Abbott, 2002,
Atmospheric Mercury Deposition during the Last 270 Years:
A Glacial Ice Core Record of Natural and Anthropogenic Sources
Environmental Science and Technology, Volume 36, No. 11, pp. 2303-2310.

Schuster, P.F., White, D.E., Naftz, D.L., and Cecil, L.D., 2000,
Chronological refinement of an ice core record at
upper Fremont Glacier in south central North America.
Journal of Geophysical Research, Vol. 105, p. 4657-4666.

Naftz, D.L., D.D. Susong, P.F. Schuster, L.D. Cecil, M.D. Dettinger, R.L. Michel, and C. Kendall. 2002.
Ice core evidence of rapid air temperature increases since 1960 in alpine areas of the Wind River Range, Wyoming, United States.
Journal of Geophysical Research, Vol. 107, No. D13, 10.1029/2001JD000621