Hold those lighters aloft: Fifty years ago this weekend, 200,000 rock fans descended on Ontario for California Jam, a one-day music festival on the grounds of the Ontario Motor Speedway. The April 6, 1974 event — ticket price: $10 — had this concert lineup, in order of appearance: Rare Earth; Earth, Wind and Fire; the Eagles with guest Jackson Browne; Seals and Crofts; Black Oak Arkansas; Black Sabbath, led by Ozzy Osbourne; Deep Purple; and Emerson, Lake and Palmer. If you’re keeping track, that’s two names with “Earth,” two with “Black” and one with “Purple.” Plus one “Browne.” Imagine 200,000 people — essentially the entire present-day population of Fontana, and more than double a Coachella Festival weekend — gathering in Ontario for a rock festival. At the time, California Jam was said to have been the largest one-day gathering in state history. ABC Entertainment produced Cal Jam and aired highlights over four nights. Showbiz professionals put on this rock festival, not idealistic amateurs. There were no breakout stars or touchstone cultural moments. Some, like reader Ron Vander Molen of Pomona, fondly recall how Keith Emerson