This kind of river typically has little to no alluvium mantling the bedrock over which it flows. Such rivers are common in upland and mountainous regions. They are formed by incision into bedrock by a combination of abrasion as sediment in the flow collides with the channel bed and removes bits of material, and "quarrying" or "plucking" as large blocks of bedrock are pulled from the bed (often near ledges and waterfalls) and sent downstream.