Caption continues: "… as Central Pacific forces were building the western link of the first transcontinental railroad, now a part of the Southern Pacific System. Rail layers, shown in the foreground, were followed by gangs of Chinese laborers who spaced and spiked the rail to the ties. A track laying record was set in April, 1869, when a picked gang of Irish rail layers, backed by a small army of truckmen, completed more than ten miles of track in one day. Please credit: Southern Pacific Compnay. From : Association of American Railroads, Transportation Building, Washington, D.C."