U.S. Route 101 (US 101) is a major north–south United States Numbered Highway, stretching from Los Angeles, California, to Tumwater, Washington. The California portion of US 101 is one of the last remaining and longest U.S. Routes still active in the state, and the longest highway of any kind in California. US 101 was also one of the original national routes established in 1926. Significant portions of US 101 between the Los Angeles area and the San Francisco Bay Area follow El Camino Real, the commemorative route connecting the former Alta California's 21 missions.

Greater Los Angeles is the most populous metropolitan area in the U.S. state of California, encompassing five counties in Southern California extending from Ventura County in the west to San Bernardino County and Riverside County in the east, with Los Angeles County in the center, and Orange County to the southeast. The Los Angeles–Anaheim–Riverside combined statistical area (CSA) covers 33,954 square miles (87,940 km2), making it the largest metropolitan region in the United States by land area. The contiguous urban area is 2,281 square miles (5,910 km2), whereas the remainder mostly consists of mountain and desert areas. With a population of 18.4 million in 2024, it is the second-largest metropolitan area in the country, behind New York, as well as one of the largest megacities in the world.