Guyana the dryer savannah areas in the south-west; and the smallest interior lowlands (interior savannah) consisting mostly of mountains that gradually rise to the Brazilian border. Some of Guyana's highest mountains are Mount Ayanganna (), Monte Caburaí () and Mount Roraima ( – the highest mountain in Guyana) on the Brazil-Guyana-Venezuela tripoint border, part of the Pakaraima range. Mount Roraima and Guyana's table-top mountains (tepuis) are said to have been the inspiration for Sir Arthur Conan Doyle's 1912 novel "The Lost World". There are also many volcanic escarpments and waterfalls, including Kaieteur Falls which is believed to be the largest water
American Falls Dam the present American Falls Dam formed a reservoir in which more than of sediments (clay, silt, and sand) were deposited. This series of basalt flows and original sediments were covered by the new lake bed sediments and are named the Snake River Group and the American Falls Lake Beds. These events occurred up until the late Pleistocene, less than one million years ago. The Snake River has continued to erode its channel in the basalt and modify the lake bed sediments until the present time. The dam at American Falls is on the Snake River Plain at an elevation of