The history of Diamond Bar CA dates all the way back to the 1840s, when California belonged to Mexico. The land that the city currently occupies was included in a land grant known as Rancho de Los Nogales. After a few more decades, this big ranch was broken up into smaller ranches, including the Diamond Bar Ranch which ultimately gave the city of Diamond Bar CA its name. Today Diamond Bar CA has come a long way since its agricultural days, and it even features some high-tech installations like the first hydrogen fueling station in Southern California.