The Tepuis are table-like mountains found only in the Guiana highlands. These geological formations tend to be found as isolated entities rather than in mountain range fashion, which makes them the host of a unique array of endemic plant and animal species. Some of the most outstanding tepuis are Autana, Neblina (the highest one, on the Venezuelan-Brazil border), Auyantepui and Monte Roraima. They are typically composed of Precambrian sandstone rocks, very hard to climb, that rise abruptly from the jungle, giving rise to spectacular natural scenery. Auyantepui in particular is the source of Angel Falls, the world's tallest waterfall.