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 to the north. To survey the rockfall and determine how to prevent the falls from becoming a series of rapids, the U.S. Army Corps of Engineers blocked the flow of water over the American Falls from June to November 1969. Results conflict as to whether tourist attendance that season was higher or lower than normal. Attendance increases were likely due to the news the cataract was dried off; decreases in tourists could be attributed to people believing both cataracts (the American and Horseshoe Falls) were dewatered. By December 1969, water was flowing over the American Falls again. In the mid‑1970s,