The road through The Bentonite Hills, along Hartnett Road to Cathedral Valley, Capitol Reef NP. Bentonite, a type of clay, is a denatured or weathered volcanic ash. Because of their excellent colloidal and absorptive properties some kinds are used for drilling mud, fining or clarifying wine, as bulk laxative and in skin products, or as the basis for cat litter. The kind found here is of poor quality and useless for such applications. When wet, the bentonite turns to slick mud and this road becomes impassable to all vehicles. If it rains while you are on this road, you stop and wait for the road to dry before proceeding!!