Tropical savannas extend throughout the majority of northern South America (Brazil, Venezuela, Colombia, Guyana, Surinam, and French Guiana). Vegetation composition ranges from closed woodland with distinct understory grass and shrub layers to open savannas and include the cerrados and campos cerrados (semi-deciduous tropical woodland), campos sujos and campos limpos (tall grass savanna), caatinga (deciduous thorny xerophytic woodland), llanos (palm savanna), and grassy savannas. Sandstone is the primary geological formation underlying the tropical savannas and the preservation of old planation surfaces is largely responsible for the continuous nature of the vegetation types.