Orinoco Basin

…to the south, the river basin covers an area of about 366,000 square miles (948,000 square km). It encompasses approximately four-fifths of Venezuela and one-fourth of Colombia.

The Orinoco River basin is nearly coextensive with the Llanos. It lies between the Venezuelan Andes and the Guiana Highlands and is covered with alluvia brought down by the Andean torrents.

The river basin, as a geomorphological feature, dates from the Quaternary Period (i.e., the past 2.6 million years). The enormous quantities of material produced by the highland regions are carried down by torrential rains to the rivers. The rivers, unable to hold the excessive material, overflow or…