Rancho Cucamonga is a city located just south of the foothills of the San Gabriel Mountains and Angeles National Forest in San Bernardino C…Rancho Cucamonga is a city located just south of the foothills of the San Gabriel Mountains and Angeles National Forest in San Bernardino County, California, United States. About 37 mi east of Downtown Los Angeles, Rancho Cucamonga is the 28th most populous city in California. The city's seal, which centers on a cluster of grapes, alludes to the city's agricultural history including wine-making. The city's proximity to major transportation hubs, airports, and highways has attracted the business of several large corporations, including Coca-Cola, Frito-Lay, Big Lots, Mercury Insurance Group, Southern California Edison, and Amphastar Pharmaceuticals.