Somerset is predominantly a rural and agricultural county. The main upland areas are the Mendip Hills in the east and the Quantock Hills further west, the Blackdown Hills form the county's southern border, and Exmoor is on the western fringes. Between the Mendips and the Quantocks is the large area of flat, low-lying ground known as the Somerset Levels. The county's main rivers are the River Axe in the northeast, and the Rivers Brue and Parrett which flow northwestward through the levels into the Bristol Channel.