Guiana Highlands, plateau and low-mountain region of South America located north of the Amazon and south of the Orinoco River. Comprising a heavily forested plateau, they cover the southern half of Venezuela, all of the Guianas except for the low Atlantic coastal plain, the northern part of Brazil, and a portion of southeastern Colombia. They are geologically similar to the Brazilian Highlands, from which they are separated by the eastern part of the Amazon lowland. The terrain comprises a mixture of three ascending elements: a basement of rolling hilly upland, standing mostly less than 1,000 feet (300 metres) above sea level; low mountains, near stream divides, ranging from 2,000 to 3,000 feet (600 to 900 metres) above sea level; and tabular plateaus, capped with resistant sandstone. The highest elevations are formed by the tabular plateaus, such as Mount Roraima (9,094 feet [2,772 metres]), where the boundaries of Brazil, Venezuela, and Guyana meet. The Guiana Highlands extend westward across the Upper Orinoco.The whole region receives an abundance of rainfall, and no season is really dry. The vegetation is mostly tropical rainforest, but parts of southern Venezuela and Guyana are savanna. From the forests come valuable cabinet woods, balata, chicle, vanilla, insecticides, and medicinal plants. The crystalline rocks carry a wealth of minerals, but exploration is made difficult by the heavy plant cover. GOLD and diamonds are mined, and the Serranía Imataca of Venezuela is a major source of iron ore.The most notable natural landmark in the highlands is Angel Falls, the world’s highest waterfall (3,212 feet [979 metres], with a base of 500 feet [150 metres]), on an affluent of the Caroní River in Venezuela.