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Thermopolis Hot Springs
Hell's Half Acre
Discover the Geology of Sinks Canyon
On the eastern slope of the Wind River Mountains abutting the city of Lander, a river mysteriously vanishes
underground only to reappear 2,000 feet, as the crow flies, downstream. The unique geologic enigma is known as the “Sinks”
and is the namesake of Sinks Canyon.
Near the entrance of the canyon, the Middle Fork of the Popo Agie River disappears into a cave
in the 330-million-year-old Mississippian Madison Limestone. The cave is part of a karst system,
which is a series of underground lakes, caves, and aquifers formed by dissolution of limestone
by groundwater. The river re-emerges less than a mile downstream and on the other side of the
highway at the “Rise.” The calm pool of water is home to huge rainbow trout.
The Middle Fork of the Popo Agie River begins high in the Wind River mountain range and cuts its way down to Lander. U.S.
Geological Survey scientists in 1983 set out to determine whether the water at the Rise was
the same water that flowed into the Sinks. They poured rhodamine dye into the water at the
Sinks and discovered that it took two hours to pass from the Sinks to the Rise. They also found
more water flows out of the Rise than into the Sinks, and the water is warmer when it comes out
of the Rise. This phenomenon remains a mystery.
More information about the Sinks and Sinks Canyon can be found on the following websites:
Wyoming State Parks Historic Sites & Trails
Sinks Canyon Natural Resource Council
Blackstone, D.L., Jr., 1988, Traveler’s guide to the geology of Wyoming (2d ed.):
Geological Survey of Wyoming [Wyoming State Geological Survey] Bulletin 67, 130 p., 13 pls.
Sinks Canyon Natural Resource Council, 2017, Nature–The sinks and rise, accessed February 2017,
Wilson, J.F., Jr., and Rankl, J.G., 1996, Use of dye tracing in water-resources investigations in Wyoming, 1967-94: U.S. Geological Survey Water-Resources Investigations Report 96-4122, p. 62.
Christina George (307) 766-2286 Ext. 231