This primary source comes from the Records of the office of the Chief of Engineers.
Full Citation: Map of Location of Central Pacific Railroad of California from Sacramento to Big Bend of Truckee, Theodore Judah, Chief Engineer; 1861; Roads; Civil Works Map File, 1818 - 1947; Records of the office of the Chief of Engineers, Record Group 77; National Archives at College Park, College Park, MD. [Online Version, https://docsteach.org/documents/document/map-central-pacific-railroad-of-california, November 8, 2024]