The chuckwalla is a large, flat, and rather chunky lizard with loose folds of skin on its neck and sides. Its tail has a blunt tip and broad base. In southern Utah, adults retain their juvenile patterns and coloration with light crossbars on the body. They are often seen sprawled on rocky outcrops basking in sun. When disturbed, chuckwallas puff themselves up by gulping in air and wedging tightly in a rock crevice. They are usually found in the lower elevations of the Reserve on rocky hillsides, outcrops and lava flows. They are primarily herbivores, eating a variety of desert plants, but they occasionally eat insects as well.