The southernmost part of the Shasta Route, all of which is now part of the Union Pacific system, is shared with the line to Donner Pass, as far as Roseville, east of Sacramento. (SP’s Shasta Route passenger trains used to turn north at Davis and follow the West Valley line to Tehama, now owned and operated by regional railroad California Northern.) The Amtrak Coast Starlight uses the East Valley line from Roseville to Tehama. Most of the Oakland to Roseville section was constructed by the Central Pacific, some of it as part of the first transcontinental line during the 1860s, and most of it as the “Cal-P” line a little later. The massive bridge over the Carquinez Strait wasn’t built until the 1930s. North of Roseville as far as Black Butte, the line was built by the Central Pacific in the 1870s and 1880s. The original line headed for Oregon over the Siskiyou Mountains, a route operated today by shortline Oregon & California. The ‘Natron Cutoff’ heading northeast from Black Butte, through Klamath Falls, Oregon, then north to Chemult and northwest across Cascade Summit to Springfield Junction, east of Eugene, OR, was built in the 1920s to ease the operating difficulties inherent in the Siskiyou line and shorten the overall distance for through trains to points north of Eugene.