bajada

Bajada is a geomorphological term used to describe a broad, gently sloping surface at the base of mountain fronts in arid and semiarid regions. The term comes from Spanish, meaning descent, and it refers to an apron-like landscape formed by the coalescence of multiple alluvial fans created by episodic streams and flash floods descending from the mountains.

Formation and characteristics: As water and sediment flow down from the range, they deposit fan-shaped fans at the mouths of valleys. Over time, successive debris flows and sediment deposits from many streams merge, producing a continuous, inclined surface that slopes away from the range. The bajada typically lacks a single trunk drainage; rather, runoff infiltrates or channels into various arroyo-type channels within the apron. The surface is often covered by a mix of gravel, cobbles, and desert pavement, with sparse vegetation.

Relation to other landforms: An alluvial fan is the individual fan-shaped deposit at the mouth of a single stream. A bajada, by contrast, is the broader, cohesive apron formed by the merging of multiple fans. Bajadas may grade gradually into adjacent plains and can be interrupted by faulting, tilting, or differential erosion, creating a stepped or irregular appearance in places.

Distribution and significance: Bajadas are common in deserts and drylands worldwide, including the southwestern United States, northern Mexico, parts of the Andes forelands, the Sahara, and other arid regions. They influence hydrology, drainage patterns, and land-use planning, and can be zones of rapid change during flash floods or debris flows.