California State Route 20
|Defined by S&HC § 320|
|Maintained by Caltrans|
|Length:||211.882 mi (340.991 km)
(plus about 15.5 mi (25 km) on US 101)
|History:||State highway in 1910-1919; numbered in 1934|
|West end:||SR 1 in Fort Bragg|
| US 101 in Willits
I-5 in Williams
SR 99 in Yuba City
SR 49 in Nevada City
|East end:||I-80 near Emigrant Gap|
California State Route 20 (SR 20), commonly known as Highway 20 or 20, is a state highway in the northern central region of the U.S. state of California, running east–west across the state north of Sacramento. Its west end is at SR 1 in Fort Bragg, from where it heads east past Clear Lake, Colusa, Yuba City, Marysville, and Nevada City to I-80 near Emigrant Gap, where eastbound traffic can continue on other routes to Lake Tahoe or Nevada.
Portions of SR 20 are built near the routing of what was first a wagon road and later a turnpike in the late nineteenth century. This road was extended through the state highway system all the way to Ukiah in the early twentieth century, and the missing link near Clear Lake was completed in 1932 before the official designation of this highway as SR 20 in 1934. There have been subsequent improvements to the road, such as the conversion of the Grass Valley portion of the route to freeway standards.
Route description 
State Route 20 east of US 101 is part of the California Freeway and Expressway System, although it is mostly a two-lane surface road. All of SR 20 is on the Interregional Road System, a highway system that connects major economic centers of the state, and has been selected by the California Department of Transportation (Caltrans) as a High Emphasis Route and Focus Route from US 101 to SR 29 and SR 53 to I-80, with the designated corridor following SR 29 and SR 53 around the south side of Clear Lake. It is also eligible for the State Scenic Highway System from SR 1 to SR 16 and SR 49 to I-80, and has been designated as such for 6 miles (10 km) near the east end; this is part of the federally-designated Yuba-Donner Scenic Byway, a National Scenic Byway that uses SR 20 east of SR 49.
State Route 20 begins at SR 1 in southern Fort Bragg, under a mile (1/2 km) from the Pacific Ocean. It heads east, quickly climbing into the Mendocino Range along a ridge and crossing through Dunlap Pass. The highway continues to rise alongside the North Fork Big River and tributaries, crossing another summit and then descending to Willits in the Little Lake Valley via Broaddus Creek. An overlap with US 101 begins in Willits and heads southeasterly to Calpella, north of Ukiah in Redwood Valley. There SR 20 turns east again, crossing the Russian River, passing the north shore of Lake Mendocino, and rising to a summit via the East Fork Russian River and Cold Creek. The roadway again descends alongside the Blue Lakes and Scotts Creek to the junction with SR 29 and the settlement of Upper Lake in the Clear Lake Basin[disambiguation needed]. SR 20 closely follows the northeast shore of Clear Lake, staying right above the water line to avoid the adjacent hills. Where the lake ends, SR 20 continues east, intersecting SR 53 and then following the North Fork Cache Creek and tributaries to the Lake-Colusa County line. During its final descent into the Sacramento Valley, SR 20 intersects SR 16 and curves north and back east, entering the valley via Salt Creek.
Once it enters the flat Sacramento Valley, SR 20 takes a generally straight path, crossing I-5 in Williams, overlapping SR 45 near the west bank of the Sacramento River southeast from Colusa, and then turning back east to cross the Sacramento River and Sutter Bypass on its way to Yuba City. The route crosses SR 99 west of central Yuba City, and runs east through northern Yuba City to the Feather River, which it crosses on the 10th Street Bridge into Marysville. Within the central part of that city, SR 20 makes several turns, first turning south from 10th Street onto E Street, then east on 9th Street (overlapping SR 70), north on B Street, and east on 12th Street (splitting from SR 70). The highway leaves Marysville to the northeast, paralleling the Yuba River on its north side as it enters the foothills of the Sierra Nevada.
SR 20 rises into the Sierras along the north side of the Yuba River, crossing to the south side near Smartville and then climbing through several ravines to the Penn Valley. The current alignment, built in the mid-1980s as a mostly two-lane freeway, continues east across rugged terrain to the city of Grass Valley, where it joins SR 49 on the Golden Center Freeway. The two routes travel northeast to Nevada City, where SR 49 turns northeast and SR 20 resumes its eastward course. The roadway climbs from Nevada City and follows Harmony Ridge and Washington Ridge before descending into the Bear Valley via a series of hairpin turns, and then climbing, just north of Emigrant Gap, to its end at I-80 at Yuba Pass. The Pioneer Trail, a National Recreation Trail, parallels SR 20 from a point on Harmony Ridge to the Bear Valley, and includes parts of a branch of the California Trail first used in 1850.
The east end of SR 20, from Bear Valley (just below Emigrant Gap) to Nevada City, closely follows a branch of the Truckee Route of the California Trail, first used by California-bound emigrants in 1850. Later a turnpike was built here by the same company that opened the Pacific Turnpike (Culbertson Road and Bowman Lake Road between Dutch Flat and Bowman Lake) in 1864.
By the end of the 1910s, a passable dirt and gravel road connected Ukiah and Nevada City via the south side of Clear Lake and Marysville. The portion between Lower Lake and Wilbur Springs was impassable in wet weather, at which times the Bartlett Springs and Bear Valley Toll-road via Upper Lake and Bartlett Springs was available for $1.50 each way or $2.50 round trip. This route generally followed the present SR 20, except around Clear Lake and between Marysville and Rough and Ready (where it used Spenceville Road). Beyond Nevada City to Emigrant Gap, the old turnpike was not passable; instead the present SR 174 was available for eastward drivers. Between Williams and Colusa, the road was paved in concrete, as it had been added to the state highway system as part of the first (1910) bond issue, specifically as Route 15, connecting the west Sacramento Valley trunk (Route 7, now I-5) with the county seat of Colusa.
This state highway was significantly extended in both directions in 1919, west to Ukiah and east to Emigrant Gap, creating what was known as the Tahoe-Ukiah Highway, connecting Ukiah and Lake Tahoe in combination with Route 37 (now I-80) and Route 38 (now SR 89). The law that defined the extension simply stated that it would connect "Ukiah to Tahoe City"; the state decided in September 1925 that it would run the highway along the north shore of Clear Lake, combining with the planned Rumsey-Lower Lake Highway (Route 50, now SR 53 and SR 16) east to Wilbur Springs. With the completion of this segment in mid-1932, the highway was ready for heavy travel, and became Sign Route 20 in 1934 as part of the initial signed state route system.
In 1953, the legislature added an extension of Route 15 from US 101 at Willits (north of Ukiah) west to SR 1 near Fort Bragg. This was constructed (over an existing county road) and became part of Sign Route 20 prior to 1964, when the Route 20 designation was legislatively adopted. Subsequent improvements include the construction of the Golden Center Freeway, connecting Grass Valley with Nevada City, in the late 1960s, and a new alignment of SR 20 west from Grass Valley, bypassing Rough and Ready, in the mid-1980s.
Major intersections 
Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. R reflects a realignment in the route since then. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.
|Fort Bragg||R0.00||SR 1 – Fort Bragg, Casper|
|US 101 north (South Main Street) / South Street – Eureka||West end of US 101 overlap|
|West end of freeway on US 101|
|R32.63[N 1]||557||West Road – Redwood Valley|
|Calpella||East end of freeway on US 101|
|US 101 south – Ukiah||Interchange; east end of US 101 overlap|
|33.77||Road 144 – Redwood Valley (Redwood Valley Rancheria)||Interchange|
|R38.05||Potter Valley Road – Lake Pillsbury|
|3.63||Scotts Valley Road|
|8.32||SR 29 – West Shore Resorts, Lakeport, Kelseyville|
|Upper Lake||8.79||Main Street – Upper Lake Business District, Ranger Station, Lake Pillsbury|
|12.20||Lakeport Cutoff, Pyle Road|
|31.62||SR 53 – Clearlake, Lower Lake, Middletown|
|Wilbur Springs||3.45||SR 16 – Rumsey, Brooks, Woodland|
SR 20 Bus. east (E Street)
|R21.85||Old Highway 99W, 7th Street (I-5 Bus.) – Williams||Interchange; former US 99W|
|R22.12||I-5 – Redding, Sacramento||Interchange|
SR 20 Bus. west (Husted Road) / Freshwater Road
|Colusa||31.09||SR 45 north (Market Street) / 10th Street – Princeton||West end of SR 45 overlap|
|36.79||SR 45 south – Grimes||East end of SR 45 overlap|
|Yuba City||15.57||SR 99 – Chico, Sacramento|
|16.33||Live Oak Boulevard, Olive Street||Live Oak Boulevard was former US 99E|
|10th Street Bridge over Feather River|
|Marysville||I Street, J Street||Interchange; no access across SR 20; J Street accessible westbound only|
|0.99||SR 70 south (E Street) / 9th Street – Sacramento||West end of SR 70 overlap|
|1.47||SR 70 north (B Street) – Oroville||East end of SR 70 overlap|
|R7.89||Loma Rica Road|
|13.27||CR E21 (Marysville Road) – Browns Valley, Dobbins, La Porte, Collins Lake, Bullards Bar Reservoir, Brownsville|
|R4.65||Pleasant Valley Road – Lake Wildwood, Bridgeport, French Corral|
|R6.60||Rough and Ready Highway – Rough and Ready, Penn Valley|
|Grass Valley||R12.16||McCourtney Road, Mill Street||Interchange|
|R12.24||SR 49 south / Empire Street – Auburn||Interchange; west end of SR 49 overlap|
|West end of freeway|
|R12.92||182A||SR 174 – Colfax, Grass Valley|
|R13.61||182B||Idaho Maryland Road, East Main Street – Grass Valley|
|R15.92||185A||Gold Flat Road, Ridge Road||Signed as exit 185 westbound|
|Nevada City||R16.74||185B||Sacramento Street – Nevada City||Eastbound exit and westbound entrance|
|186||Broad Street, Coyote Street – Nevada City|
|East end of freeway|
|R17.40||SR 49 north / Uren Street – Downieville||East end of SR 49 overlap|
|45.66||I-80 – Auburn, Sacramento, Truckee, Reno||Interchange|
- Indicates that the postmile represents the distance along US 101 rather than SR 20.
- California Department of Transportation, State Truck Route List (XLS file), accessed January 2008
- California State Legislature, CA Codes (shc:163-164.56), accessed March 2008
- California Department of Transportation, High Emphasis Routes, January 2005
- California Department of Transportation, Focus Routes, January 2005
- California Department of Transportation, Route 20 - Scenic Highway, accessed January 2008
- National Scenic Byways Online, Yuba-Donner Scenic Byway, accessed January 2008
- Google Maps street maps and USGS topographic maps, accessed January 2008 via ACME Mapper
- U.S. Forest Service, Pioneer Trail, revised May 2006
- California Highways and Public Works: Centennial Edition, September 9, 1950, p. 64
- Official Automobile Blue Book, Volume Eight, 1919, pp. 146-147, 176-178, 225-226, 231
- Automobile Club of Southern California, Automobile Road Map of California, 1917
- Howe & Peters, Engineers' Report to California State Automobile Association Covering the Work of the California Highway Commission for the Period 1911-1920, pp. 11-16
- Ben Blow, California Highways: A Descriptive Record of Road Development by the State and by Such Counties as Have Paved Highways, 1920 (Archive.org or Google Books), pp. 104-105
- California State Legislature (1919). "Senate Constitutional Amendment No. 27—Resolution to propose to the people of the State of California an amendment to the constitution of said state, by adding to article sixteen thereof a new section to be numbered two, providing for the issuance of bonds to the amount of forty million dollars for the completion of the state highway system and the acquisition and construction of other state highways by the state department of engineering". State of California. 1919 resolution chapter 46, p. 1520.
- Oakland Tribune, Highway Commission Lays Plans for Building Lake Connection, September 6, 1925
- Fresno Bee, Route Follows Lake Shore, September 27, 1925
- Cass Kennedy, Oakland Tribune, Tahoe-Ukiah Highway Ready for Heavy Travel, March 6, 1932
- California Highways and Public Works, State Routes will be Numbered and Marked with Distinctive Bear Signs, August 1934
- California State Legislature (1953). "An act to amend Section 315 of the Streets and Highways Code, relating to the State Highway System". State of California. 1953 chapter 1408, p. 3002.: "Route 15 is from Route 56 near Fort Bragg to Route 37 near Emigrant Gap via Willits, Calpella, Williams and Colusa."
- H.M. Gousha Company, California, 1955
- H.M. Gousha Company, California, 1963
- California State Legislature (1963). "An act...relating to routes on the state highway system". State of California. 1963 chapter 385, p. 1173.: "Route 20 is from: (a) Route 1 near Fort Bragg to Route 101 at Willits. (b) Route 101 to Route 80 near Emigrant Gap via Williams and Colusa."
- California Department of Transportation, Log of Bridges on State Highways, July 2007
- California Department of Transportation, All Traffic Volumes on CSHS, 2005 and 2006
- California Department of Transportation, California Numbered Exit Uniform System, State Route 20 Freeway Interchanges, Retrieved on 2009-02-05.
- California Department of Transportation, California Numbered Exit Uniform System, U.S. Route 101 Freeway Interchanges, Retrieved on 2009-03-21.