Located in the northwest corner of North America and geographically separated from the contiguous United States, Alaska shares an eastern border with Canada. The state can be broadly divided into five main geographical regions. The Pacific mountains includes the Alaska Range and the fjords and islands of the southeastern Panhandle. North of the Alaska Range is a plateau consisting of rolling hills and the flat Yukon River Basin. To the north rises the Brooks Range and, beyond that, the North Slope, a flat coastal plain that slopes down to the Arctic Ocean. Stretching away in the southwest of the Alaska are the Aleutian Peninsula and Islands, a volcanic arc that forms part of the Pacific Ring of Fire.

Alaska Range

The Alaska Range curves through the south-central region of Alaska. It includes Denali (formerly Mount McKinley), at 6190 metres (20,310 feet) the highest peak in North America. Along with other ranges in southern Alaska, it is made up of pieces of crust, known as terranes, pushed together over the past 100 million years by the Pacific plate as it moved towards the North American continental plate. When the continents collided, the terranes piled up on top of each another, pushing the land upwards.
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During the Pleistocene Ice Ages, an ice sheet ground slowly across the Alaska Range, carving deep, U-shaped valleys. When the ice melted and sea levels rose, ocean waters flooded these deep valleys, creating the fjords and islands, the Alexander Archipelago, of the southeastern Alaska Panhandle.

Interior

Between the Alaska Range to the south and the Brooks Range to the north are the rolling hills and low-lying plains of Alaska's Interior. Over millions of years, rivers have filled the depressions between the ranges with eroded sediments carried down from the mountains. In this way, flat plains, such as the Yukon River Basin, were created.

North Slope

A plain slopes gently down from the Brooks Range northwards to the Arctic Ocean. The Arctic Coastal Plain, often called the North Slope, is a flat, featureless expanse. An ancient seabed that has been uplifted by tectonic forces, it is covered by permafrost, soil that remains frozen year-round. In summer, it becomes a wetland with thousands of shallow peat lakes and tundra vegetation.

Aleutians

The Aleutian Range, which extends into the Aleutian Islands in the southwest, is a 2400-kilometre (1500-mile) volcanic arc. As the Pacific plate sinks beneath the continental plate, its rocks melt deep within the Earth's mantle. Magma, molten rock, rises to the surface through cracks in the crust, erupting as volcanoes. The Aleutian Peninsula and, beyond that, the Aleutian Islands, are the product of this volcanic activity, dating back more than 50 million years.