A slot canyon is a narrow canyon, formed by the wear of water rushing through rock. A slot canyon is significantly deeper than it is wide. Some slot canyons can measure less than one metre (3 ft) across at the top but drop more than 30 m (100 ft) to the floor of the canyon. Most slot canyons are formed in sandstone and limestone rock, although slot canyons in other rock types such as granite and basalt are possible. Even in sandstone and limestone, only a very small number of creeks will form slot canyons. This is due to a combination of the particular characteristics of the rock, and regional rainfall. -Wikipedia