You have a unique opportunity to see the different geologic formations during your drive through the canyon. The youngest formation, about 280 millon years old is called Phosphoria and is at the top of the cliffs to your right. The Pre-Cambrian granite of over 600 million years ago is exposed at the bottom of the switchbacks about 4 miles from this point.

There is also evidence of the glacial action that was once a part of this area, including polishing and striation of rocks, glacial erratics or the large boulders carried down from higher elevations and deposited here as the glaciers melted, and the moraines or glacial debris (rocks and fine silt) left in long piles. You can see a medial moraine cross section revealed during road construction between the Visitor Center and Popo Agie Campground. Look for the road cut where you see the widest variety of rock sizes and types.

This canyon is a young one, and yet it shows us millions of years of rocks formations, exciting evidence of the glaciers and of the Sinks—where the Popo Agie River disappears into a cavern formed by erosion only to reappear in a trout filled pool called the Rise.

Source: Wyoming Recreation Commission