In pre-Columbian times, the Eastern Cordillera of Colombia was densely forested up to altitudes of at least 3,000 metres. Spanish colonists and land-hungry mestizos cleared the forests and cultivated the steep slopes with maize and cassava. Rain washed the fertile humus layer down into the valleys until the bare gneiss was exposed over a wide area. Today, vast masses of scree fill the valleys, where rivers meander between gravel banks, as is the case here with the Rio Chicamocha in the department of Santander. - Book: Picture 20 - Colombia - 1977