The Juneau International Airport is located in southeast Alaska. Juneau is unique among the 49 U.S. capitals on mainland North America in that there are no roads connecting the city to the rest of the state or North America. The absence of a road network is due to the extremely rugged terrain surrounding the city. Downtown Juneau sits at sea level, below steep mountains about 3,500 to 4,000 feet (1,100 to 1,200 m) high. Atop these mountains is the Juneau Icefield, a large ice mass from which about 30 glaciers flow; two of these, the Mendenhall Glacier and the Lemon Creek Glacier, are visible from the local road system.