Washington State Route 20
East-west state highway in Washington, US
State Route 20 (SR 20), also known as the North Cascades Highway, is a state highway that traverses the U.S. state of Washington. It is the state's longest highway, traveling 436 miles (702 km) across the northern areas of Washington, from U.S. Route 101 (US 101) at Discovery Bay on the Olympic Peninsula to US 2 near the Idaho state border in Newport. The highway travels across Whidbey Island, North Cascades National Park, the Okanagan Highland, the Kettle River Range, and the Selkirk Mountains. SR 20 connects several major north–south state highways, including Interstate 5 (I-5) in Burlington, US 97 through the Okanogan–Omak area, SR 21 in Republic, and US 395 from Kettle Falls to Colville.
SR 20's path across the Cascades follows one of the oldest state roads in Washington, established in 1896 as a wagon route. The wagon road fell into disuse within a decade, and the state government postponed the construction of a new route across the North Cascades for several decades. The development of the Skagit River Hydroelectric Project spurred boosters to lobby the state for a new route across Washington Pass, which was opened in 1972. SR 20 originally ran from the Mount Vernon area to Okanogan. By 1973, SR 20 was extended over existing state highways in northern Washington, replacing SR 113 and portions of SR 525 and SR 536 near Port Townsend; SR 30 and SR 294 from Tonasket to Tiger; and part of SR 31 from Tiger to Newport.
Although US 12 has a larger east–west extent, SR 20 is the longest highway in Washington at 436.13 miles (701.88 km), only 5.3 miles (8.5 km) longer than US 12.
The public source identifies “Washington State Route 20” as east-west state highway in Washington, US. This brief keeps that definition visible, then builds a research path around Washington, State and Route.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jul 21, 2026. The linked authority identifier is Q835817. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank. The first chronological checks are 1896, 1972 and 1973.
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This entry incorporates text from “Washington State Route 20” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.