Boulders and rock piles are a distinctive attraction of Joshua Tree National Monument's geologic landscape. Their fantastic shapes and their warm color are an invitation to dream and fantasy... or to rock climbing.<br><br>These huge vertical stones are made of hard granite, and their smooth shapes is the result of an erosion and weathering process that started when the rock was still below the ground level, millions of years ago, and continued through times of important rainfalls: the sculpture-like features of the boulders are mainly the work of water before the local climate turned arid.
