The result is downcutting of small canyons, called washes or arroyos . Basin and Range Topography A. Alternating uplifted and down-dropped normal fault blocks can produce a landscape of mountain ranges separated by broad basins. If such tectonic activity occurs in arid regions, internal drainage networks are common. Not enough water flowing through streams to provide for downcutting of drainage divides. Water does not flow to the sea, but rather collects in basins, or low points in the landscape.
Streams flowing from bedrock-confined canyons carved in the mountains have a high capacity.
The wetted perimeter of the unconfined flow is much greater, resulting in friction that reduces stream velocity and triggers aggradation. 3. where a long, linear mountain range has many adjacent canyons, alluvial fans will build and coalesce with neighboring fans, producing a broad apron of sediments at the base of the mountains known as a bajada . This causes coarser sediment load to be deposited near the top of the bajada surface, with finer textured materials remaining in suspended load and washing out into the adjacent basin. Also, water pools in lowlands after heavy rains, then slowly evaporates. These salt-encrusted low points in the center of drainage basins are called alkali flats , or playas .