Bajada (geography)

A bajada consists of a series of coalescing alluvial fans along a mountain front. These fan-shaped deposits form from the deposition of sediment within a stream onto flat land at the base of a mountain. The usage of the term in landscape description or geomorphology derives from the Spanish word bajada, generally having the sense of "descent" or "inclination".

When a stream flows downhill it picks up sediment along with other materials, as that stream emerges from a mountain front the sediment begins to deposit. The coarser sediment falls out closest to the base and the finer sediment grades outwards and deposits in a fan-shape away from the mountain face. The sediment is transported across a pediment into a closed basin where the bajadas grade back into a pediment, making the boundary difficult to distinguish. Bajadas frequently contain playa lakes. Bajadas are common in dry climates (i.e. the Southwestern US) where flash floods deposit sediment over time, although they are also common in wetter climates where streams are nearly continuously depositing sediment.

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