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Bajada or Bahada

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Bajada (Spanish: slope), also spelled as bahada, consists of a series of coalescing alluvial fans along a mountain front. Such fan-shaped deposits are formed by the deposition of sediments within a stream resting on the flat land at the base of the mountain. The term “ Bajada” is widely used to detail the landscape of geomorphology. 

What are Bajadas?

Bajadas are the shallow slopes that lie at the base of the rocky mountains, where the material gets accumulated from the weathering of the rocks. The bajadas typically have a mixture of sand, gravels, boulders, and silt particles, forming a  deep and complex soil structure that holds water and supports rich vegetation. 

Bajada Formation

When a stream slopes downwards, it picks up sediments along with the other material. As the stream comes up from a mountain front, the sediments that are carried begin to be deposited, such that the rough deposits are deposited at the base and the finer deposits arranged outwards in a fan - shape away from the mountain base. The sediments are further transferred to the opposite side of pediments into a close basin where the bajadas are arranged back into the pediments, making the boundary difficult to observe. 

Bajada Occurrence

Bajadas are moderately sloping depositional plains located between playa and pediments. They are commonly found in dry climates ( for example the Southwest US) where the flash flood deposits remain over time. Bajada is also commonly found in wetter climates where streams are almost constantly depositing sediments. 

Did You Know?

  • Bajadas below the Hexie Mountains can be seen from Joshua Tree National park.

  • Bajadas are found on both sides of Death valley (north of Stopevilles Wells), more well developed on the Panamint Range side.

  • A bajada is generally composed of gravel alluvium and even has larger rocks interbedded in it.

  • Pyara lake is found between the Bajadas and pediments.

  • The Spanish term Bajada means inclination or descent is often used to describe a landscape or geomorphology.  

  • When many alluvial fans come together at one place, or deposits in the same area it forms bajada. Due to the gathering of all the fans, it implies that there is much more water and sediments than usual, and is quite evenly spread out to the whole bajada.

FAQ (Frequently Asked Questions)

1. What are Alluvial Fans?

Ans: An alluvial fan is triangular-shaped deposits of gravels, sand, and fine materials known as alluvium. Alluvial fans are usually formed as flowing water interacts with mountains, hills, or steep walls of canyons. Streams carrying alluvium can be a powerful river, a fast-moving creek trickles of rainwater, or even runoff from agriculture or industry. As a stream flows down to the hill, it carries sand and other particles with it known as alluvium. The flowing water further carries alluvium to a flat plain, where the stream leaves its channels to spread out. The alluvium is deposited as a streaming fan out, forming a  triangle-shaped feature. 

2. What are Pediments?

Ans: In Geology, the pediment is a relatively flat bedrock surface that is formed at the base of the mountain or as a plain having no associated mountain.  Pediments are developed when a sheet of running water( sheet flood) wash it over massive rainfall events. Pediments are thinly covered with Fluval gravel that has washed over it from the foot of the mountain obtained by cliff retreat erosion. The pediment is not to be messed with the bajada which is a merged group of alluvial fans. Bajada is gently sloped from mountain ranges, that consist of material eroded from canyons in the crop and re-deposited as bajada, instead of bedrock with a thin veneer of gravel.

3. What is Playa?

Ans: Playa lakes, also known as flat or dry lakes are a type of shallow wetland that usually forms after massive rainfall. They are usually found in the interior desert basin adjacent to the coast with arid and semi-arid regions, periodically covered by water that slowly evaporates into the atmosphere or filters into the groundwater system., causing the deposition of sand, salt, and mud along the bottom and around the edges of the depression.  The dry lakes by this name are found in the western United States and Mexico.