Well removed from the Pacific Ocean, Interstate 8 lowers to Sea Level in the Imperial Valley of California. 01/27/06
The lowest freeway in the country at one point (as it drops below sea level in the Imperial Valley near El Centro), Interstate 8 also traverses several mountain passes en route between San Diego, California, and Casa Grande, Arizona. Beginning in the Ocean Beach neighborhood, I-8 proceeds east along an urban course through the San Diego metro area. Beyond El Cajon and Alpine, the freeway winds through Cleveland National Forest and Laguna Mountain range before angling southeast. I-8 passes through the In-ko-pah Gorge ahead of Ocotillo and the rolling desert hills and farmland in the Imperial Valley. The freeway enters Arizona at the Colorado River and Yuma, and advances east across more desert terrain, including the famed Arizona saguaro. I-8 concludes at I-10 midway between Phoenix and Tuscon.
Interstate 8 only intersects one U.S. route for its entire length, U.S. 95, thus lending credibility to the paucity of U.S. highways in the Southwestern United States. However, it parallels a well-preserved historic U.S. route, Old U.S. 80.
U.S. 80 follows Interstate 8 from San Diego to Gila Bend, Arizona, where U.S. 80 turned north along what is now Arizona Route 85 to Interstate 10 near Buckeye. Well-preserved stretches of Highway 80 are otherwise accessible as frontage roads and county roads along the freeway corridor.
The easternmost stretch of I-8 between Gila Bend and Casa Grande was not a former U.S. route; the Interstate instead replaced former SR 84. (A shorter section remains close to Casa Grande.)
Origins of Interstate 8 in San Diego date back to 1957 with construction for a new U.S. 80 freeway between U.S. 395 and Ward Road. The majority of the U.S. 80 freeway was completed east from U.S. 101 to El Cajon by the early 1960s, with I-8 formally posted in 1964. Originally, I-8 was planned to end at Interstate 5. However, with the construction of the Ocean Beach Freeway (former California State Route 109), the route was extended west to the intersection of Nimitz Drive and Sunset Cliffs Boulevard.
The Pine Valley Creek Bridge opened to traffic in 1975. This segmental balanced cantilever bridge carries the freeway over 200 feet above the valley floor.1 A more detailed history for I-8 posted at the Interstate 8 California guide.
Within Arizona, the earliest sections of Interstate 8 completed ran between Sentinel (Exit 87) and Piedra (Exit 102) and from Gila Bend (Exit 119) to SR 84 (Exit 151) in 1959. The Colorado River bridge west of Yuma opened in 1979 as the last portion of I-8 opened overall. See the Interstate 8 Arizona guide for a more detailed time line.
The lowest point on the entire Interstate Highway System (excluding underwater tunnels) is located on Interstate 8 at this point, when the freeway crosses the New River at an elevation of 52 feet below sea level. The lowest point is located near Exit 107 (Drew Road), which is west of El Centro in California’s Imperial Valley. Further west, I-8 climbs to over 4,000 feet above sea level to cross the Cuyamaca Mountains. 01/27/06