Much of Tucson's economic development has been centered on the development of the University of Arizona, which is currently the second largest employer in the city. Davis-Monthan Air Force Base, located on the southeastern edge of the city, also provides many jobs for Tucson residents. Its presence, as well as the presence of the US Army Intelligence Center (Fort Huachuca, the largest employer in the region in nearby Sierra Vista), has led to the development of a significant number of high-tech industries, including government contractors, in the area. The city of Tucson is also a major hub for the Union Pacific Railroad's Sunset Route that links the Los Angeles ports with the South/Southeast regions of the country.