The WSA is characterized by features resulting from erosion of the multi-colored sedimentary rocks of the eastern San Rafael Swell, including the slopes of the San Rafael Reef on the eastern edge of the WSA: vertical cliffs, buttes, ridges, alcoves, and pinnacles. The San Rafael River has cut deeply in the southeastern portion of the WSA to form narrow, deep canyons known as the Upper and Lower Black boxes. Large isolated erosion remnants such as Mexican Mountain are distinctive in the southeastern part of the WSA. The ruggedness of the terrain contributes to its suitability as nesting habitat for raptors, such as golden eagle and prairie falcon, habitat for desert bighorn sheep, and scenic interest. The San Rafael River runs through the WSA, cutting deep canyons and providing an important perennial water source with its riparian vegetation.