A lot of places and businesses around Concord are named some variation on "Black Diamond". This name makes reference to coal, which used to be mined around the area. The Black Diamond coal mines operated from 1861 until circa 1900. Between 1867 and 1883 they produced over 100,000 tons of coal every year. Coal was hauled by horse and rail over to river landings where it was loaded on barges.
Miners and families from Mt. Diablo coal towns crossed Mt. Diablo Creek for supplies, services, and recreation. It was a very "Wild West" kind of place where brothels and drinking establishments like inns and saloons outnumbered other kinds of businesses.