The uppermost formation, recognized by its light color and massive cliffs is the Tensleep Sandstone. The black and red streaks on the face of the cliffs are oxides of iron and manganese and are called “desert varnish.” The next formation is the Amsden Formation but is difficult to see because it has eroded to a grass and tree-covered slope. Below this is Madison Limestone. Through this soft formation the Sinks and Rise occur. Water enters through fractures 1/4 mile upstrem at the Sinks, then moves laterally down through the formation These geologic features create the unique wildlife habitats found at Sinks Canyon.

Limestone can be dissolved by carbonic acid, a weak, naturally-forming acid created by the combination of water and carbon dioxide. This acid dissolves the limestone and continued water movement will create channels in the stone. In this fashion the Sinks were created. The water reappears here through small fractures around the sides of the pool and in the sandy bottom.