Granite Dells, just north of Prescott, Arizona, is a distinctive granite landscape of exposed bedrock, rounded boulders, and smooth domes surrounding Watson Lake and Willow Lake. Its Precambrian granite formed about 1.4 billion years ago when a pluton intruded deep below the surface, then was exposed as overlying rock eroded away. Weathering along joints, especially spheroidal weathering, produced the area’s lumpy, rippled forms. The granite’s high uranium content can make radon a concern for nearby homes. The area also preserves regional railroad history through the Peavine National Recreation Trail and Iron King Trail, both converted from former rail lines.