arroyo

An arroyo is a dry creek or stream bed with nearly vertical walls. Arroyos are ephemeral water ways, and so remain dry most of the time, but can fill and flow with water after a large amount of rainfall. Although they are often naturally created when riverbeds overflow and then dry out again, cutting into the rock outside the streambed, in many desert regions, arroyos are also constructed and used as a means of flood control and irrigation. Arroyos exist throughout the western United States, but are most common in the arid and semi-arid climates of the Southwestern U.S.