#alluvial fan

In the mountains you can get a lot of two things, rocks and sediments produced from the break down of those rocks. In the foreground and in the background around the feet of the mountains you can see two big piles. These are called alluvial fans. It is basically a dump of sediments that was flushed down the small valleys into a big valley. What runs between these two alluvial fans is a major river which is a conveyor belt of the sediment that slowly moves it down the valley, down the mountains, down the floodplains and eventually into the ocean.

See it as a highway for moving of sediment.

Nubra River, Himalaya.