California Jam was a music festival co-headlined by Deep Purple and Emerson, Lake & Palmer, held at the Ontario Motor Speedway in Ontario, California, on April 6, 1974. Produced by ABC Entertainment, it attracted an estimated 400,000 people. The festival set what were then records for the loudest amplification system ever installed, the highest paid attendance, and highest gross in history.
It was the last of the original wave of rock festivals, as well as one of the most well-executed and financially successful, and presaged the era of media consolidation and the corporatization of the rock music industry. Other acts included Black Sabbath, Seals & Crofts, Black Oak Arkansas, The Eagles, Rare Earth and Earth, Wind & Fire.