Most of the country is low-lying, with a maximum altitude of c.200 ft (60 m). However, the southeast, which forms a small part of the Fouta Djallon region, rises to c.1,400 ft (430 m). Senegal's coast (c.250 mi/400 km long) is sandy from Saint-Louis to Dakar, situated near the tip of the Cape Verde peninsula, and is swampy or muddy south of Dakar. The country is mostly covered with savanna, which becomes semidesert in the Sahel region of the north and northeast; the southwest is forested. The chief rivers of the country are the Senegal (which forms the boundary with Mauritania), the Falémé, the Gambia (Fr. Gambie ), and the Casamance. Lake Guiers is located in the north. In addition to Dakar, other cities include Diourbel, Kaolack, Louga, M'Bour, Rufisque, Saint-Louis, Thiès, Touba, and Ziguinchor.