Interstate 15 (I-15) is a major Interstate Highway in the western United States. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Canada, passing through the states of California, Nevada, Arizona, Utah, Idaho, and Montana. The interstate serves the cities of San Diego, Las Vegas, St. George, Salt Lake City, Pocatello and Butte. It also passes close to the urban areas of Orange County, California, Los Angeles County, California, Ogden, Utah, and Helena, Montana.