Zion National Park's 2,000-foot sandstone cliffs are world renowned for their big wall climbs. Due to their difficulty, most routes in the park are not recommended for inexperienced climbers. There not many top roping and sport climbing areas. The best conditions for climbing are from March through May and September through early November. Temperatures in the summer can soar over 100 degrees on unshaded walls. Sandstone is weak when wet. Avoid climbing in damp areas or after rain. Afternoon thunderstorms are common in July and August.