Trails James Beckwourth opened the
Beckwourth Trail over
Beckwourth Pass in 1851, crossing the
Sierra Nevada at a lower elevation than the existing
Donner Pass route of the
California Trail. This split from the
Truckee Route of the California Trail near
Reno and roughly followed the present SR 70 to
Quincy, but, rather than passing through the Feather River Canyon, it followed Oroville-Quincy Highway along ridges to
Bidwell's Bar. A company was incorporated on July 23, 1855, to build the
Quincy and Spanish Ranch Wagon Road, which bypassed the older trail from Quincy west to
Spanish Ranch and began collecting
tolls in November. The
Pioneer Wagon Road, another toll road, was built in 1856 and 1857, continuing the improvements southwest to Buckeye (just before the
Butte County line). An 1866 law authorized
Plumas County to improve the portion from Quincy east to
Beckwourth. The county also improved the road east from Beckwourth over the pass as part of the
Red Clover Wagon Road, which began at
Genesee and was completed in the 1870s. The
Western Pacific Railroad completed its main line into California in 1909. This followed the old Beckwourth Trail east of Quincy, but to the west it reached
Oroville and
Marysville via the
Feather River Canyon. While building the railroad, the
Utah Construction Company had created a dirt road through the canyon to assist with construction; citizens created the Plumas County Road Association in 1911 to push for improvements to this roadway and creation of a year-round route between Oroville and Quincy (the existing route over the ridges was closed for at least four months each winter). The first state highway bond issue, passed by the state's voters in 1910, included a Route 30 connecting Oroville with Quincy.
Plumas County surveyor Arthur W. Keddie surveyed the Feather River Canyon route for the
California Highway Commission in 1913, but the state announced in 1916 that the existing ridge route would be improved. After much debate, the state legislative road committee included the statement that this route would follow the Feather River in the 1919 amendment authorizing a third bond issue; instead of keeping it as Route 30, the Highway Commission changed the designation to an extension of the short
Richvale-
Oroville (now
SR 162) Route 21, which was also part of the first bond issue.
Modern route Construction began on July 1, 1928, with
convict labor for the easier portions and
contractors for the remainder, as well as bridges and tunnels, but was slowed by the
Great Depression. On the most difficult portion, between Cresta and Rock Creek, three tunnels had to be built at Arch Rock, Grizzly Dome, and Elephant Butte; at the former two,
surveyors had to hang out on rope over steep
granite slopes, and
rockslides repeatedly caused delays. The commission dedicated the road at a ceremony at Grizzly Dome, halfway between the ends, on August 14, 1937. Construction had cost $8.15 million for 78 miles (126 km) of new road. The remainder of the old trail from Quincy to the junction with
Route 29 (now
U.S. 395) east of Beckwourth Pass was added to the state highway system in 1931 as an extension of Route 21, and was paved by 1936. Route 87 from Woodland to Oroville and Route 21 from Oroville to east of Beckwourth Pass became a new
State Route 24 in 1934; State Route 24 was extended southwest from Woodland to
Oakland by the end of 1937.
U.S. Route 40 Alternate In 1954, the original part of State Route 24 was replaced by U.S. Route 40 Alternate, which continued south on
U.S. 99W from Woodland to
Davis and southeast on
U.S. 395 to
Reno, Nevada to join
U.S. 40 at both ends. A direct route from Marysville south to
Sacramento was added to the state highway system in 1949 as Route 232, and later became part of a rerouted State Route 24. The U.S. 40 Alternate designation was short-lived, and was mostly replaced by State Route 70 in the
1964 renumbering. Southwest of Marysville, former U.S. 40 Alternate instead became
State Route 113, and SR 70 ran south along former State Route 24 (Route 232) to a point north of Sacramento, where the new
State Route 99 came in from the northwest and continued south. Despite SR 70 always ending at State Route 99, it was once signed along State Route 99 (El Centro Road, Garden Highway, and the
Jibboom Street Bridge) to Sacramento.
Modern alignments When it was originally built, the Feather River Highway northeast from Oroville followed the present Oroville Dam Boulevard (
County Route B2) to the present location of the
Oroville Dam, and then ran north and northeast alongside the North Fork Feather River along a route now covered by
Lake Oroville. It left to the north on Dark Canyon Road, meeting the present alignment at
Jarbo Gap. Since the old road would be flooded, a $14.8 million new alignment, much of it four lanes, was built around the west side; the Western Pacific Railroad was also relocated to a nearby alignment. The double-decker
West Branch Bridge over the
West Branch Feather River northwest of the dam, carrying the highway above the rail line, was dedicated on August 15, 1962. Three portions of SR 70 have been upgraded to
freeways: north of
SR 99 to Berry and Kempton Roads in the early 2010s; south from
Marysville to the
State Route 65 split in the mid-1950s, extended farther south in the late 1960s and late 2000s; and around downtown
Oroville, built in the early 1960s. A freeway interchange was constructed in 2008 at Plumas Lake Boulevard for access to the
Plumas Lake development previously served at an uncontrolled intersection with Plumas Arboga Road. The removal of this intersection effectively upgraded the expressway portion to freeway south to the Feather River Boulevard intersection. In the early 2010s, the last two-lane segment of SR 70 south of Marysville was expanded to a four-lane expressway, with a freeway section bypassing the small town of
East Nicolaus to the west. In 2015, the interchange with Feather River Boulevard in Plumas Lake was opened to traffic, eliminating the last signalized intersection between Sacramento (with SR 99) and Marysville. In 2023, one of the last stretches of two-lane highway of SR 70, between East Gridley Road and just north of Laurellen Road, was widened to a four-lane expressway, with a
center left-turn lane and eight foot wide shoulders on each side. The project was completed in September of that year. The portions between SR 162 and East Gridley Road were completed in the early 2010s to the early 2020s.
Future The last two-lane section of SR 70 between Marysville and Oroville, which involves the portion between 14th Street in Marysville and Laurellen Road just north of Marysville was approved to be expanded into four lanes, with a center left-turn lane. It will involve expanding the narrow roadway under two railroad overcrossings and the relocation of a levee. The project is on hold as the city of Marysville is in a lawsuit with Caltrans over the increased traffic through the city. Once the project is completed, SR 70 will become a continuous four-lane highway from its start at SR 99 all the way to SR 191 south of Paradise, even though traffic will still have to navigate through the center of Marysville. ==Major intersections==