[1] It is the largest sedimentary basin of Venezuela of Quaternary origin, since the large volumes of sediments, which are fundamentally alluvial, were deposited during the last two million years of the geological history of the planet.

It extends between the Guiana Shield, to the south; the Venezuelan Coastal Range to the north; and the Cordillera de Mérida to the west.

At the bottom of this primitive interior sea giant quantities of organic matter were accumulated, formed by animal and plant remains.

In it are located the petroleum basins of Barinas-Apure and the Oriental, which includes the Orinoco Belt, also the coal-basins of Guárico and Anzoátegui.

Los Llanos, therefore, are a broad plain, very flat or slightly undulating, that descends gently from north to south and from east to west, that is, from the mountainous alignments of the Cordillera de Mérida and the Sierra del Interior of the Caribbean Mountain System to the Orinoco river, to the south and the Atlantic Ocean to the east.