worth mentioning are the Apure, Arauca, Caura, Meta, Barima, Portuguesa, Ventuari and Zulia, among others. The country's main lakes are Lake Maracaibo -the largest in South America- open to the sea through the natural channel, but with fresh water, and Lake Valencia with its endorheic system. Other noteworthy bodies of water are the Guri reservoir, the Altagracia lagoon, the Camatagua reservoir and the Mucubají lagoon in the Andes. Navigation in Lake Maracaibo through the natural channel is useful for the mobilization of oil resources. Relief The Venezuelan natural landscape is the product of the interaction of tectonic plates that since the Paleozoic have contributed to its current appearance. On the formed structures, seven physical-natural units have been modeled, differentiated in their relief and in their natural resources. The relief of Venezuela has the following characteristics: coastline with several peninsulas and islands, adenas of the Andes mountain range (north and northwest), Lake Maracaibo (between the chains, on the coast); Orinoco river delta, region of peneplains and plateaus (tepui, east of the Orinoco) that together form the Guyanas massif (plateaus, southeast of the country). The oldest rock formations in South America are found in the complex basement of the Guyanas highlands and in the crystalline line of the Maritime and Cordillera massifs in Venezuela. The Venezuelan part of the Guyanas Altiplano consists of a large granite block of gneiss and other crystalline Archean rocks, with underlying layers of sandstone and shale clay. The core of granite and cordillera is, to a large extent, flanked by sedimentary layers from the Cretaceous, folded in an anticline structure. Between these orographic systems there are plains covered with tertiary and quaternary layers of gravel, sands and clayey marls. The depression contains lagoons and lakes, among which is that of Maracaibo, and presents, on the surface, alluvial deposits from the Quaternary, on layers of the Cretaceous and Tertiary particularly important; because of them oil infiltrations emerge. The coasts They present a landscape with intermountain depressions (separated by mountains), mountainous areas, a massif and an island group. Lara-Falcón-Yaracuy System The reliefs of mountain ranges contrast with those of the peninsula, coastal plains and intermountain depressions. Lake Maracaibo Basin The basin of the lake and the plains of the Gulf of Venezuela make up two plains: the northern one, drier, and the southern one, humid and with swamps. The Andes The corpulent volumes of mountain ranges and mountain ranges