As with many Southern California communities, Diamond Bar's recorded history began with a Mexican land grant. On March 30, 1840, Governor Juan Alvarado deeded 4,340 acres, which included Brea Canyon and the eastern Walnut Valley, to Jose de la Luz Linares, who founded Rancho Los Nogales, or Ranch of the Walnut Trees. Linares died in 1847, and his widow sold a choice portion of the ranch to Ricardo Vejar for $100 in merchandise, 100 calves, and the assumption of her late husband's debts. Vejar already owned the Rancho San Jose to the east (now Pomona), and by acquiring the rest of Rancho Los Nogales over the next ten years, became the fifth wealthiest landowner in Los Angeles County, with over 10,000 acres.

The Ontario International Airport is only twenty-five minutes away, giving Diamond Bar residents an attractive alternative to Los Angeles International Airport. A two-hour drive lands you beside the waters of Lake Arrowhead, or in the snowy mountains of Big Bear. Whether you prefer the hills and canyons in the city, the nearby mountains, the sun on the surf, or the desert, Diamond Bar places you at the center of the active Southern California life-style.