The Alaska Peninsula is a peninsula on the mainland of Alaska at the beginning of the Aleutian Islands. It extends southwest from the Alaska mainland for about 800 km (500 miles) between the Pacific Ocean and Bristol Bay, an arm of the Bering Sea. The Aleutian Range of volcanic mountains runs along its entire length. It contains the Katmai National Park and Preserve, the Aniakchak National Monument and Preserve and the Becharof National Wildlife Refuge , the Alaska Peninsula National Wildlife Refuge, and Izembek National Wildlife Refuge .