The Rockhounder: Gypsum sand near Knolls, Tooele County

By Christine M. Wilkerson

Geologic information:

Gypsum sand dunes are widespread on the eastern margin of the Great Salt Lake Desert. Gypsum dune sand can be collected near Knolls in Tooele County. Sandsize gypsum (calcium sulfate with water) crystals form in the top layer of the moist, salty clay that forms the desert floor. As the clay dries, the gypsum crystals are blown by the wind into dunes. These dunes also contain many oolites: small, rounded grains of calcium carbonate layered around a tiny brine shrimp fecal pellet or mineral fragment. These oolites formed in the Great Salt Lake approximately 9,400 to 9,700 years ago when the lake was larger and its shoreline was located in the Knolls area at an elevation of about 4,230 feet.

How to get there:

Travel approximately 78 miles west of Salt Lake City on Interstate 80 until you reach the Knolls exit. Exit and turn south (left) onto the frontage road to Knolls. Travel about 1.5 to 2 miles. Sand dunes are located on both sides of the road.

Where to collect:

Gypsum sand dunes are adjacent to the road and easily accessible in this area. Use a plastic bag or a bucket to collect the sand. Be careful not to disturb the vegetation that stabilizes the dunes.

Useful maps:

Bonneville Salt Flats 1:100,000-scale topographic map, Knolls 7.5-minute topographic map, and a Utah highway map. Topographic maps can be obtained from the Utah Geological Survey, 1594 W. North Temple, Salt Lake City, UT 84114-6100, (801) 537-3321.

Land ownership:

Bureau of Land Management (BLM) public lands.

Miscellaneous:

A hat and water are recommended. Glasses will protect your eyes from wind-blown sand. Watch out for broken bottles and shotgun shells. Please carry out your trash. Have fun collecting! For information on where to collect oolitic sand, see “The Rockhounder”, Survey Notes v. 28 no. 2.

Survey Notes, v. 28 no. 3, May 1996