I-8

About I-8

Also known as Kumeyaay Highway.

From San Diego, CA (I-5) to Casa Grande, AZ (I-10)

Interstate 8 is a southern east-west route running about 348 miles from San Diego, California, to Casa Grande, Arizona, where it ends at Interstate 10. From its western terminus near the Pacific it climbs over the mountains east of San Diego, drops into the Imperial Valley, crosses the Colorado River at Yuma, and continues across the deserts of southwestern Arizona to the Phoenix area's southern approaches.

The corridor passes through some of the hottest and most arid terrain in the country, including stretches of sand dunes near the California-Arizona line and long desert basins. It serves border-region agriculture in the Imperial Valley and around Yuma, and it functions as a direct route between coastal Southern California and south-central Arizona that stays well south of I-10.

State-by-state mileage

State	Miles
California	171.9
Arizona	178.3
Total	350.2

History

Interstate 8 was designated in 1957 as part of the original Interstate system and was built largely along the corridor of older U.S. Route 80 across the southern California and Arizona deserts. Construction included challenging mountain segments in the Cuyamaca and In-Ko-Pah ranges east of San Diego.

The route was completed in stages over the following decades, replacing the older two-lane desert highway with a modern divided freeway.

Major cities and places

Notable features

• Imperial Sand Dunes
• Colorado River crossing at Yuma
• In-Ko-Pah Gorge

Did you know

• It connects the San Diego coast directly with south-central Arizona through the desert.
• The highway crosses the Imperial Sand Dunes near the California-Arizona border.
• It crosses the Colorado River at Yuma between California and Arizona.
• The route follows much of the path of historic U.S. Route 80.