easternmost group of the Aleutian Islands, southwestern Alaska, U.S. The islands extend about 300 miles (500 km) southwest from the Alaska Peninsula and are part of the extensive Alaska Maritime National Wildlife Refuge. The island group includes Akutan, Unalaska, and Umnak; Unimak Pass, separating the Fox Islands from Unimak Island, is one of the principal navigational lanes in the Aleutians. The largest settlement of the Aleutian Islands and one of the top fishing ports in the United States is Unalaska (Dutch Harbor) on the island of Unalaska. The mountainous islands contain several active volcanoes, including Makushin Volcano (6,680 feet 【2,036 metres】) on Unalaska Island and Okmok Caldera (3,520 feet 【1,073 metres】) on Umnak Island. The chain is sparsely populated, with fishing as the primary economic activity.