The September 1959 issue of Road & Track offers an interesting article on the California racing scenes and participants for the movie. They were shot at Riverside in September 1958. Originally scheduled to take a tight five days, the scenes ended up requiring ten days of shooting.
Some of the drivers used in the Riverside scenes are well known: Dan Gurney in a Corvette, Bobby Drake in the #5 Monza, Max Balchowsky [of Old Yaller fame] in a Buick-engined Doretti, Jerry Austin in a D-type and Skip Conklin in a Lotus 11. Also participating were Bob Bondurant, Eric Hauser and Mary Davis. Skip Hudson drove a Corvette with camera man Bob Johanas strapped in the passenger seat.
The crashes were done by three of Hollywoods best stunt professionals: Cary Loftin, Harvey Perry and Dale Van Sickle, although realistic dummies were used in some of the scenes. Engines and transmissions were typically removed from the cars that were to be wrecked.