Island Mountain

Island Mountain in southwestern Trinity County, California, is a resistant volcanic and metavolcanic mass whose island-like enclosure by the Eel River and nearby creeks gave it its name in the 1850s. Its durability forced the river into a sharp S-curve and made the mountain a defining feature of the landscape. It later became crucial to the Northwestern Pacific Railroad, which crossed the river there and passed through tunnel 27 on the route to Eureka, completed in 1914. Rail access also supported mining and quarrying, while a 1978 tunnel fire and collapse led to costly rebuilding finished in 1979.

California · United States