Sheltered valleys in the Atlas Mountains, the Nile Valley and Delta, and the Mediterranean coast are the main sources of fertile farming land. A wide variety of valuable crops including cereals, rice and cotton, and woods such as cedar and cork, are grown. Typical Mediterranean crops, such as olives, figs, dates and citrus fruits, also thrive in these areas. The Nile Valley is particularly fertile and most of the population in Egypt live close to the river. Elsewhere, irrigation is essential to improve crop yields on the desert margins.