In the Central American Republic of El Salvador the Rio Lempa divides the eastern third of the country from the rest. In its lower course it flows through a large coastal plain, built up in geologically recent times by river deposits and sediments from the volcanic chain in the north (San Vicente and the volcanic group of the east). From west (Balsam range) to east (Colinas de Jucuarán) this plain has a length of about 100 km. and a width of 20 km. Some 20 years ago the nearly flat land, which slopes only very slightly from the volcanic chain to the Pacific coast, was still heavily wooded, but since then most of the forest has been cleared away for cotton crops, only leaving tiny patches of the original vegetation. In this process a number of archaeological sites were revealed, especially east of the Rio Lempa, in the department of Usulután.