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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,〔California State Legislature, (CA Codes (shc:163-164.56) ), accessed March 2008〕 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.〔California Department of Transportation, (High Emphasis Routes ), January 2005〕〔California Department of Transportation, (Focus Routes ), January 2005〕 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;〔California Department of Transportation, (Route 20 - Scenic Highway ), accessed January 2008〕 this is part of the federally designated Yuba-Donner Scenic Byway, a National Scenic Byway that uses SR 20 east of SR 49.〔National Scenic Byways Online, (Yuba-Donner Scenic Byway ), accessed January 2008〕 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. 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.〔Google Maps street maps and USGS topographic maps, accessed January 2008 via (ACME Mapper )〕 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 Smartsville 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 northwest and SR 20 resumes its eastward course as a two-lane highway. 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「California State Route 20」の詳細全文を読む スポンサード リンク
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