Unalaska, rugged island, 30 mi (48 km) long, off SW Alaska, one of the largest Aleutian Islands. Visited (c.1759) by Russian explorers, the island was a center of Russian fur trade until it was superseded by Kodiak. Spruces planted on Unalaska by the Russians remain among the few trees in the Aleutians. The main towns on the island are Unalaska and Dutch Harbor.