The Alaska Peninsula is a peninsula extending about 800 km (500 miles) to the southwest from the mainland of Alaska and ending in the Aleutian Islands. Along with the Aleutians, is serves to separate the Pacific Ocean from Bristol Bay, an arm of the Bering Sea.
The southern-most side of the Alaska Peninsula is rugged and mountainous, created by the uplifting tectonic activity of the North Pacific Plate subsiding under a western section of the North American Plate; whereas the northern side is generally flat and marshy, a result of millennia of erosion and general seismic stability.