Depositional Features and Landforms
Alluvial fans are fan-shaped piles of sediment that form where a rapidly flowing mountain stream enters a relatively flat valley. As water slows down, it deposits sediment (alluvium). As the stream migrates back and forth in the open valley, the sediment gradually builds a fan.
Bajadas are are aprons of rocky debris that form when alluvial fans coalesce to form a ramp that spreads out toward the valley floor. A bajada or piedmont slope partially buryies the range front in its own sediment.
Stream terraces are long bench-like surface bordering a stream or wash. A terrace is a level or near-level area of land above a water course and separated from it by a steeper slope. A stream terrace is made by the stream at some time in the past when the river flowed at a higher level. A terrace may be made of stream deposits such as gravel or sand, or it could be an erosional cut by the stream on bedrock.
Playas are shallow, short-lived lakes that form where water drains into basins with no outlet to the sea and quickly evaporates. Playas are common features in arid (desert) regions and are among the flattest landforms in the world.
Basins are depression in the Earth’s surface that collect sediment. Rock particles that wash down from mountain sides collect in adjacent basins, in some places burying the bedrock under thousands of feet of rock debris.