Primary route
I-15
San Diego to the Canadian border
Length1,433.1 mi
Designated1957
States6
Junctions9
About I-15
Also known as Mojave Freeway, Ronald Reagan Freeway.
From San Diego, CA (I-8) to Sweetgrass, MT (Canada border)
Interstate 15 is a major north-south route of the interior West, running about 1,433 miles from San Diego, California, to the Canadian border at Sweetgrass, Montana. It passes through six states, crossing Southern California, the Mojave Desert, the Las Vegas valley in Nevada, the populated Wasatch Front of Utah, and the open country of Idaho and Montana. It is a primary corridor for travel between Southern California and the Intermountain West.
The route links San Diego, the Las Vegas area, Salt Lake City, and the smaller cities of Idaho and Montana, while serving heavy recreational and freight traffic between California and the mountain states. It crosses several mountain passes and high basins, climbing well away from the desert lowlands into the elevated valleys of Utah and the northern Rockies. Through Utah it follows the densely settled Wasatch Front for many miles.
Interstate 15 carries auxiliary routes serving its larger urban areas, including beltway and spur routes in the Las Vegas and Salt Lake City regions. Across the deserts between metropolitan areas it runs for long, sparsely populated stretches.
State-by-state mileage
| State | Miles |
|---|---|
| California | 287.3 |
| Nevada | 123.8 |
| Arizona | 29.4 |
| Utah | 400.6 |
| Idaho | 196.0 |
| Montana | 396.0 |
| Total | 1,433.1 |
History
Interstate 15 was designated in 1957 as part of the original Interstate system and was built over many years, replacing older highways such as U.S. Route 91 through much of its course. Construction included desert segments across the Mojave and mountain crossings in Utah, Idaho, and Montana.
The corridor has been progressively widened, especially along the Wasatch Front and through the Las Vegas valley, to keep pace with rapid growth in those regions.
Major cities and places
San DiegoSan BernardinoBarstowLas VegasSt. GeorgeProvoSalt Lake CityOgdenPocatelloIdaho FallsButteGreat FallsSweetgrass
Notable features
- Cajon Pass
- Virgin River Gorge
- Monida Pass
Did you know
- It runs from the Mexican border approaches at San Diego to the Canadian border in Montana.
- Cajon Pass in California is a key crossing between the Los Angeles basin and the high desert.
- The Virgin River Gorge in Arizona is one of the most expensive rural Interstate segments ever built.
- It follows much of the path of historic U.S. Route 91.
- The route serves both the Las Vegas valley and the Wasatch Front of Utah.