Great Salt Lake, Utah
Antelope Island
The Great Sal
t
Lake (dark blue area at top of image to the left) is located in northern
Utah. The Lake is the remnant of a much larger ice-age Lake Bonneville
that occupied most of the northwest corner of the present state. Great
Salt Lake is a closed-basin lake with no outlet for water that enters into
it except for evaporation. The light blue area just to the west of the
Great Salt Lake in this 1972 Landsat image is the the Bonneville salt
flats. The green tinted area just to the east of the Lake in
this image is the Wasatch Mountain Range.
The
more detailed map at right shows just the area of the Great Salt Lake.
There are a number of islands within the Lake, one of which Antelope Island
is tinted orange in the map at right. Antelope island is the largest
of the Great Salt Lake islands - currently it is 15 miles long and 4.5 miles
wide at its widest point.
The entire area of northwest Utah is within the Basin and Range geologic
province. Mountains (horsts) and valleys (grabens) are formed by huge
blocks of rock that are bounded by normal faults that trend roughly 
northwest in this region. The western edge of the Wasatch Mountains
(photo below) is
the eastern limit of the Basin and Range Province in this area. 
On
Antelope island a block of very old (2.7 bya) metamorphic rock lies along
the "spine" of the island (snow-covered mountains in photo at
left) with the much younger (550 mya) Tintic
quartzite (metamorphic sandstone) draped over the older rocks and found
primarily on the northern third of the island (on either side of the road in
photo at upper left).
The Great Salt Lake became a closed-basin lake about 10 to 15,000 years
ago. It dried up in stages and became increasingly 
salty until today
when it is about 10 times as salty as sea water. When there were
pauses as the Lake level
fell waves cut beach platforms which can now be
seen clearly all around the lake as semi-horizontal stand lines. These
are easily seen at several locations on Antelope island in the photos at
left and right taken near the northern edge of the island along White Rock
Bay.
Recent fluctuations in the level of the Great Salt Lake have alternately
isolated Antelope Island or re-connected it to the mainland. The Great
Salt Lake is very shallow (47 feet deep is its maximum depth) and has a
current level of about 4200 feet above sea level. Fluctuations of the
Lake over the past 150 or so years can be seen in the graph below>
Closer inspection of the stand line platforms often reveals deposits of
tufa - calcium carbonate precipitated 
from
the former Great Salt Lake water. Blocks of tufa can be seen in the
photo at bottom left taken near the visitor center at the northeast end of
the island. (In this photo you can also see the causeway that connects
Antelope Isl
and
to the mainland.) Beach sands being deposited today all around Great
Salt Lake and on Antelope Island (photo at right of Bridger Bay at the
northern end of the island) are oolitic - tiny, spherical grains of calcium
carbonate formed by concentric precipitation around nuclei that are usually
brine shrimp fecal pellets. The entire area of the Lake and Antelope
Island is a desert. There are very few trees on the island and most of
the vegetation is grass (photo below) and shrubs (far right photo).
Note that the black dots in the grassland glen
photo are buffalo - part of a herd of about 500 to 700.
The Bingham Canyon Mine
Just south of Antelope Island on the mainland near the town of Magna (see
detailed map above) is the Bingham Copper Mine - 
the
largest copper mine in the world. The photo at right is an air photo
of the mine showing the
excavation pit and the mounds of tailing just east of the pit (seen in photo
at left). The mine is run by Kennecott Copper (see photo below).
Although the ore body was apparently formed through contact metamorphism
with a granite intrusion the ore contains sufficient organic matter to be
self-smelting (the mine does not import any energy to extract the copper
from the ore). In addition to copper the mine extracts gold, silver, molybdenum
and cadmium. The gold is used by Tiffany's in their jewelry. 
