Land and Resources: Most of the country of Senegal is made up of plains, which lie below about 100 meters. Elevations rise to approximately 1640 feet; however, this is only present in the extreme south-east, at the foot of Fouta Djallon. Senegal also contains 3 major rivers. Senegal which forms the northern border, and Gambia, Saloum and Casamance. Climate: Most parts of Senegal alternate between a dry desert climate and a hot humid tropical climate in the south. The rainy season in this country lasts from July to October in the north with an average rainfall amount of 14 inches and from June to October with an average rainfall of 60 inches in the south. Temperatures that fall on the coastal strip range from 22°C in January to 28°C in July. Vegetation and wildlife: The northern part of Senegal is part of the Sahel, a transition zone between the northern Sahara and the humid regions of the south. The vegetation consists largely of savanna grass with scattered trees and shrubs. The vegetation south towards the Gambia River consists of many trees and further south there are mainly mangrove swamps and oil forests, mahogany, bamboo and teak. Wildlife is varied and larger animals, however, such as elephants, cheetahs, lions and antelopes are found more in the less populated eastern half of the country. Crocodiles and hippos are found in most rivers. Senegal also contains a variety of snakes such as the Cobra and the Boa constrictor. Mineral Resources: Senegal's most exploited mineral source is located near Thie's and contains that of mined phosphates. Also in the late 1970s, oil and natural gas were discovered off the coast of Senegal. Large deposits of iron have also been discovered, but not mined due to their remoteness. Agriculture: Agriculture provides employment for more than 70% of Senegal's workforce. Crops are closely linked to the seasons and the amount of rainfall. Crops in the northern part of the country are subject to the effects of rain and drought. Two different types of agriculture are practiced in Senegal.