Sinks State Park
South of Lander

“The Sinks” are a series of cracks and crevices at the back of the cavern before you. The water of the Popo Agie River flows into the Sinks. It then reappears at the “Rise of the Sinks”, a large calm pool 1/4 mile down the canyon.

The Sinks are eroded into the soft white Madison Limestone formation. No spelunkers have explored very far into the sinks since the cracks narrow down to very small log and rock choked passages.

It is unknown exactly how old the Sinks are although they are likely an Ice-Age feature thousands of years old. The glaciers that carved the canyon exposed the soluble limestone and the billions of gallons of water from melting ice helped create the underground passages

For many years it was unknown whether the water flowing into the Sinks was the same water flowing out at the Rise. Dye test have proven the connection but have also revealed another mystery: it takes the water flowing into the Sinks over over 2 hours to reappear at the Rise. It was also discovered that more water flows out at the Rise than goes in at the Sinks. Why the water takes over two hours to make the journey and where it goes during that time is still a mystery.

The amount of water flowing into the Sinks varies throughout the year. Most of the time much of the limestone cavern is exposed and all of the river’s water flows underground through the cracks and fissures in the rock.

The average flow of the Popo Agie into the Sinks is about 100 cubic feet per second. This level drops in the winter and jumps dramaticlly during spring runoff. In late May and early June the river swells with melted snow from the mountains and the river fills the cavern completely. During run-off over 500 cubic feet per second of water flows into the cavern. The water is so high that logs and driftwood are jammed into cracks in the ceiling of the cave-high above where people stand when the water is low. The cracks in the limestone cannot handle all this extra water and the excess spills over into a seasonal streambed (called the overflow channel) to the left. Depending on how much snow is in the mountains, the Sinks can overflow from a few days to a few weeks. Every year during spring run-off there is water flowing both below and above ground between the Sinks and Rise.

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