The volcanic rocks of the Southern Absaroka Mountains are a southern continuation of the early and late volcanic units of the northern Absaroka Volcanic Field. Explosive and flow breccias, tuffs, and volcanic conglomerates are the dominant rock types of this region.
Throughout the greater part of the area the volcanics show essentially horizontal bedding, but in some areas steep dips are found. Along the eastern front of the mountains, in the vicinity of Wood River, postvolcanic deformation is reflected in dips varying between 15 and 50 degrees. The general axis of the deformation strikes north-northeast, and approximately 40 square miles have been deformed.
Numerous large intrusions, representative of a fairly normal intermediate to felsic magma, occur in a belt that may be aligned in a northwest direction with intrusions in the northern Absaroka Mountains. Locally some of the intrusions have deformed the volcanics and lifted Paleozoic formations to abnormally high elevations.
Near the divide between Wood River and the headwaters of the Wind River a small area of unusual pink volcanic breccias indicates volcanic activity which may be the time equivalent of the more recent extrusions of rhyolite and basalt in Yellowstone National Park.