The Cesar-Ranchería Basin (Spanish: Cuenca Cesar-Ranchería) is a sedimentary basin in northeastern Colombia. It is located in the southern part of the department of La Guajira and northeastern portion of Cesar. The basin is bound by the Oca Fault in the northeast and the Bucaramanga-Santa Marta Fault in the west. The mountain ranges Sierra Nevada de Santa Marta and the Serranía del Perijá enclose the narrow triangular intermontane basin, that covers an area of 11,668 square kilometres (4,505 sq mi). The Cesar and Ranchería Rivers flow through the basin, bearing their names.
The basin is of importance for hosting the worldwide tenth biggest and largest coal mine of Latin America, Cerrejón. The coals are mined from the Paleocene Cerrejón Formation, that also has provided several important paleontological finds, among others Titanoboa cerrejonensis, with an estimated length of 14 metres (46 ft) and a weight of 1,135 kilograms (2,502 lb), the biggest snake discovered to date, the giant crocodylians Cerrejonisuchus improcerus, Anthracosuchus balrogus and Acherontisuchus guajiraensis, and the large turtles Carbonemys cofrinii, Puentemys mushaisaensis and Cerrejonemys wayuunaiki. Various genera of flora, as Aerofructus dillhoffi, Menispermites cerrejonensis, M. guajiraensis, Montrichardia aquatica, Petrocardium cerrejonense and P. wayuuorum, Stephania palaeosudamericana and Ulmoidicarpum tupperi among others, have been found in the Cerrejón Formation, the sediments of which are interpreted as representing the first Neotropic forest in the world. Mean annual temperature has been estimated to have been between 28.5 and 33 °C (83.3 and 91.4 °F) and yearly precipitation ranging from 2,260 to 4,640 millimetres (89 to 183 in) per year.
