<P> The highway then tracks a little to the northeast, and I - 205 splits off south of the Portland metro area . From here I - 5 passes through Tualatin and Tigard along former U.S. Route 99W (US 99W) before hitting the southern terminus of I - 405 and the Marquam Bridge . Also planned was a spur in Portland off I - 405, called I - 505, but it was never built and has been removed from city plans . A stub of I - 505 exists as a long exit ramp to US 30 . </P> <P> After crossing the Willamette River on the Marquam Bridge, I - 5 has junctions at the western end of I - 84 and the northern end of I - 405 . It then continues through the northern parts of the city of Portland, and crosses into Washington via the Interstate Bridge . </P> <P> The highway continues over the Columbia River and drops down into the city of Vancouver . About seven miles (11 km) into the state, it reaches the northern terminus of I - 205, which is on the eastern edge of the Portland--Vancouver metropolitan area . It then tracks north by northwest through Woodland to Kelso and Longview, at which point it ceases to parallel a large bend of the Columbia River . Continuing north between the Willapa Hills and the Cascade foothills, the freeway eventually reaches Olympia, where it bends sharply east . The highway passes though the northern end of Joint Base Lewis - McChord (formerly Fort Lewis and McChord Air Force Base) and Tacoma, where it bends sharply north again to reach Seattle . The Ship Canal Bridge carries it over Portage Bay in Seattle . The freeway continues north out of the Seattle--Tacoma--Everett metro area, crosses the floodplains of three rivers, through the Skagit Valley and the Mount Vernon--Burlington Metropolitan Area to the northern city of Bellingham, to arrive at the Peace Arch Canada--US border crossing between Blaine, Washington, and Surrey, British Columbia . Highway 99 continues northwest from the border into Vancouver, BC . I - 5 covers 277 miles (446 km) in Washington . </P> <P> An extensive section of this highway (over 600 miles (970 km)), from approximately Stockton, California, to Portland, Oregon, follows very closely the track of the Siskiyou Trail . This trail was based on an ancient network of Native American footpaths connecting the Pacific Northwest with California's Central Valley . By the 1820s, trappers from the Hudson's Bay Company were the first non-Native Americans to use the route of today's I - 5 to move between today's Washington State and California . During the second half of the 19th century, mule trains, stagecoaches, and the Central Pacific railroad also followed the route of the Siskiyou Trail . By the early 20th century, pioneering automobile roads were built along the path of the Siskiyou Trail, notably the Pacific Highway . The Pacific Highway ran from British Columbia to San Diego, California, and was the immediate predecessor of much of US 99 . The route of US 99 was in turn used as a basis for much of the route of today's I - 5 . </P>

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