The Nafud is an erg, a desert region located in north-central Saudi Arabia. It is noted for its sudden violent winds, which account for the large crescent-shaped dunes. The sand in the Nafud is a brick-reddish color. Rain comes once or twice a year. In some lowland areas, namely those near the Hejaz Mountains, there are oases where dates, vegetables, barley, and fruits are raised. The Nefud is connected to the Rub' al Khali by the Dahna, a corridor of gravel plains and sand dunes, long and wide.