Sinks Canyon State Park
7 miles southwest of Lander (307) 332-6333

Sinks Canyon is so named because the Middle Fork of the Popo Agie River rushes out of the Wind River Mountains, down the canyon and then abruptly vanishes into a large cavern halfway down the canyon. The river is underground for 1/4 mile until it emerges in a large, calm pool on the other side of the canyon and then continues its course into the valley below.

The Sinks and Rise are natural occurrences that are not uncommon in limestone formations around the world. The uniqueness about the Sinks is its size and the length of time the water is underground.

The lower portion of the canyon is made up primarily of sandstone and limestone formations which are easily eroded by wind and water. The formation in which the river actually vanishes is called Madison Limestone, a massive, off-white limestone formation that is very soft and soluble.

Geologists speculate that the Sinks could have been formed in two ways: either the cavern and cracks in the limestone already existed because of earth tremors and the river found and flowed into them; or the river naturally eroded the soft limestone creating its own passage underground. It’s likely that a combination of these two events created the Sinks. For many years it was unknown if the water in the Rise was the same water flowing into the Sinks. Dye tests had been attempted on occasion but no conclusive evidence was found. In 1983 the U.S. Geological Survey and Sinks Canyon State Park staff conducted an official dye test using red dye.

The dye, called Rhodamine, was poured into the water above the Sinks and testing with a fluorometer was simultaneously started in the pool at the Rise. Samples were taken every five minutes but the first traces of dye were not detected until two hours after it had been dumped into the Sinks. When the testing was finished, nearly all of the dye had been recovered, leading the researchers to conclude that all of the water flowing into the sinks comes out at the Rise. However, two new facts were discovered during the testing: 1) MORE water comes out at the Rise than flows into the Sinks, and 2) the water that flows out into the Rise is a few degrees WARMER than the water entering the Sinks.

The central mystery of “where does the water go for over two hours?” has yet to be solved. Geologists speculate that there could be a large underground aquifer or lake that slows the progress of the water. There could also be a myriad of channels and passages that the water has to circulate though before it reaches the Rise. It is probable that a combination of these two geologic formations slows the progress of the water.

Rainbow Trout in the Rise
The huge trout in the Rise are not stocked. They have arrived there naturally and stay because it is a protected area with an extensive food supply. The fish are mainly Rainbow Trout, though some are Browns.

No one has weighed or measured the fish but some of the larger ones probably weigh up to 12 pounds. There is no fishing in the Rise, but visitors enjoy throwing fish food to the trout from the observation platform above the Rise.

What does Popo Agie mean?
The name Popo Agie (pronounced Po-Po Zshuh) comes from the Crow Indians and means “Tall Grass River.” “Agie” means river in the Crow language and “PoPo” means tall grass or tall rye grass. The Crow named the river this because of the tall bunches of rye grass that grew along the banks of the river in the valley.

Wildlife, Flora and Fauna
Famous for the mysterious Sinks and Rise and its spectacular geology, Sinks Canyon is the home to a myriad of wildlife, birds and plants. There are three major habitats in the canyon and each is unique. The most dramatic contrast in habitats is between the heavily forested north facing slope and the drier, sagebrush and juniper covered south facing slope.

The north facing slope is in the shade much of the winter allowing heavy snow to accumulate. This snow provides moisture needed for Limber Pine and Douglas Fir trees. Birds such as the Western Tanager, the Mountain Chickadee, Blue Grouse and Townsend’s Solitaire live in these thick, coniferous forests. Mammals such as the Pine Martin, Porcupine, Black Bear and the Red Squirrel prefer the forest. Wildflowers such as Heartleaf Arnica, Lupine and Phlox are also found.

The south facing slope receives a great deal of sunshine all winter which melts snow quickly. Lack of snow makes it excellent winter range for many animals because they don’t have to struggle to find food. Bighorn Sheep and Mule Deer are commonly seen on this rocky slope in the winter. Golden Eagles and tiny Cliff Swallows can be seen souring above the cliffs. Green-tailed Towhees and Kestrels also make this place their home. Wildflowers such as Sego Lily, Hawksbeard and Arrowleaf Balsamroot are bright splashes of color among the blue-grey sagebrush.

The third Sinks Canyon habitat is the Riparian zone along the Popo Agie River. It is the moist area along either side of the river where thick stands of Aspen, Chokecherry and Willow grow. Moose are occasionally seen in the Riparian zone browsing on Willow or Red-Osier Dogwood. Birds such as the Lazuli Bunting, the Dipper, the Rufous Hummingbird and Black-headed Grosbeak can be seen in the heavy foliage. In this moist Riparian zone are wildflowers flouris such as Sticky Geranium, Yellow Monkeyflower and Columbine.

All of these habitats make Sinks Canyon a rich place to observe nature. Surrounding National Forest and wilderness areas extend the opportunity to experience Wyoming’s beauty at its best. Remember, you are a visitor to the home of the Bighorn Sheep, Marmot and the Golden Eagle. Please respect the wildlife, observing them from a distance, and please leave the wildflowers for others to enjoy.

Reprinted from Wyoming State Parks and Historic Sites brochure.

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