considered the westernmost point of the Americas. Ponta do Seixas in northeastern Brazil forms the easternmost extremity of the mainland, while Nordostrundingen, in Greenland, is the most easterly point of the continental shelf. Geology South America broke off from the west of the supercontinent Gondwana around 135 million years ago, forming its own continent. Around 15 million years ago, the collision of the Caribbean Plate and the Pacific Plate resulted in the emergence of a series of volcanoes along the border that created a number of islands. The gaps in the archipelago of Central America filled in with material eroded off North America and South America, plus new land created by continued volcanism. By three million years ago, the continents of North America and South America were linked by the Isthmus of Panama, thereby forming the single landmass of the Americas. The Great American Interchange resulted in many species being spread across the Americas, such as the cougar, porcupine, opossums, armadillos and hummingbirds. Topography The geography of the western Americas is dominated by the American Cordillera, with the Andes running along the west coast of South America and the Rocky Mountains and other North American Cordillera ranges running along the western side of North America. The Appalachian Mountains run along the east coast of North America from Alabama to Newfoundland. North of the Appalachians, the Arctic Cordillera runs along the eastern coast of Canada. The largest mountain ranges are the Andes and Rocky Mountains. The Sierra Nevada and the Cascade Range reach similar altitudes as the Rocky Mountains, but are significantly smaller. In North America, the greatest number of fourteeners are in the United States, and more specifically in the U.S. state of Colorado. The highest peaks of the Americas are located in the Andes, with Aconcagua of Argentina being the highest; in North America Denali (Mount McKinley) in the U.S. state of Alaska is the tallest. Between its coastal mountain ranges, North America has vast flat areas. The Interior Plains spread over much of the continent, with low relief. The Canadian Shield covers almost 5 million km2 of North America and is generally quite flat. Similarly, the north-east of South America is covered by the flat Amazon basin. The Brazilian Highlands on the east coast are fairly smooth but show some variations in landform, while farther south the Gran Chaco and Pampas are broad lowlands. Climate The climate of