Of particular interest to visitors are a series of nearby maar, or phreatomagmatic craters, which are located approximately 5-10 miles to the north and east of the main spine of the range. The craters include Kilbourne Hole, Hunt's Hole, and Phillips Hole. These formations are estimated to have an age of between 24,000 and 50,000 mya. They are associated with the Potrillo volcanic field. That field includes the West Potrillo Mountains and the Aden lava flows to the north and west.