Most of the year, visitors can see deep into the limestone cave at the Sinks of the Middle Fork of the Popo Agie. But in this photo from May 30, only a small gap remains between the top of the boiling stream and the roof of the cavern. (WyoFile/Andrew Graham)

Snowmelt and a healthy dose of rain last weekend flooded the Middle Fork of the Popo Agie River with more water than the limestone cavern it flows into could contain.

The famed Sinks of the Popo Agie is a cavern entrance where the Middle Fork goes underground, flowing into a series of cracks and fissures in the limestone. The water reappears just down the canyon in a pool called the Rise — tranquil on its surface compared to the boiling mountain stream up canyon. But a closer look shows a constant upwelling of water as the Middle Fork of the Popo Agie bubbles back up from beneath.

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When streamflow is low, visitors can see well into the cave at the Sinks. But on Wednesday, only a small gap still appeared between the top of the boiling stream and the roof of the cavern. With the Sink full, water flowed into an overflow channel that only becomes active when the flows are too high for the Sink to contain.

A photo from Sinks Canyon State Park shows that when streamflow is low, the entirety of the cavern that the Middle Fork of the Popo Agie flows into is visible. (Wyoming State Parks)

Andrew Graham is reporting for WyoFile from Laramie. He covers state government, energy and the economy. Reach him at 443-848-8756 or at, follow him @AndrewGraham88

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