|South end||San Diego, CA|
|North end||Vancouver, BC|
|States||California, Oregon, Washington|
Good roads advocate and road-building pioneer Sam Hill was perhaps the main motivating force behind building the original Pacific Highway as a "national auto trail"; from Blaine, Washington, on the Canada–US border, where he would build his Peace Arch, through Oregon to the Siskiyou Mountains of northwestern California. The road was built in the early 20th century—long before the U.S. Highway System was established. In 1926, its 1,687 miles (2,715 km) of pavement made it the longest continuous stretch of paved road in the world at the time. The Pacific Highway later extended north to Vancouver, British Columbia, and south through San Francisco to San Diego in Southern California.
The Pacific Highway auto trail became British Columbia Highway 99 from Vancouver to the Canada–United States border, U.S. Route 99 from the border to Red Bluff, California, in the Sacramento Valley; U.S. Route 99W from Red Bluff to Davis, California, in the Central Valley; U.S. Route 40 from Davis to San Francisco; and U.S. Route 101 from San Francisco to San Diego. This alignment is now mostly Interstate 5 in California, except between Woodland, California, and Los Angeles, where it uses State Route 113, Interstate 80 and then U.S. Route 101.
In Oregon, Interstate 5 is now officially the Pacific Highway No. 1 (see Oregon highways and routes). First completed in 1923, Oregon's Pacific Highway was the first border-to-border paved highway west of the Mississippi River.
In California, Highway 1 named the Pacific Coast Highway or the "PCH" runs along the coast from Leggett, California (north of San Francisco) south through Big Sur to Los Angeles before terminating in Orange County. PCH runs along the coast while Pacific Highway runs inland. An old freeway section of U.S. Route 101 parallel to Interstate 5 near the San Diego International Airport is known as 'Pacific Highway' and is now locally maintained. It also runs through the North County of San Diego.
An extensive section of the Pacific Highway (over 600 miles), from approximately Stockton, California to Vancouver, Washington, followed very closely the track of the Siskiyou Trail. The Siskiyou 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 the future Pacific Highway to move between today's Washington State and "Alta 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.
In the early 20th century, around 1910, entrepreneur Sam Hill lobbied the governments of Washington and Oregon to build automobile roads along the path of the Siskiyou Trail, with the ultimate goal of building a paved auto route from Canada to Mexico.
- Hardwick, Jacque; Rose, Karen; Walker, Mike (April 11, 2010). "Pacific Highway/US 99 Milepost Brochure" (PDF). Hugo Neighborhood Association & Historical Society. p. 1. Retrieved October 11, 2012.
- Tuhy, John E. (1983). Sam Hill: The Prince of Castle Nowhere. Portland, OR: Timber Press. p. 145. ISBN 0-917304-77-2.
- Kramer, George (2004). "Interstate 50th Anniversary—The Story of Oregon's Interstates" (PDF). Oregon Department of Transportation. p. 3. Retrieved August 29, 2007.
- Official Museum of the Siskiyou Trail website
- 'Control Cities' of the Pacific Highway auto trail
- The historic Pacific Highway in Washington