When tracks were laid for the new Southern Pacific Railroad, two teams raced to join each other, one moving south through the Central Valley and the other heading north from Los Angeles. The main obstacle was the Tehachapi Mountains, outside of Los Angeles. Eighteen tunnels were required for the railroad to pass through this mountain range. The longest one, seen here, stretched for a mile and a half. After 1860, the railroad was a persistent subject in Carleton Watkins's photographs. As a close friend of Collis P. Huntington, one of the executives responsible for the creation of the Central Pacific Railroad and its extension, the Southern Pacific, Watkins traveled along the railways for many years with complimentary annual passes. He essentially functioned as an unofficial photographer of the railroads, often taking images on or near the new tracks.