The man was pronounced dead at the scene at Marysville Raceway Park some 40 miles north of Sacramento, and the boy was declared dead either at the hospital or in an ambulance, Yuba County Sheriff's Capt. Ron Johnson told the Marysville Appeal-Democrat newspaper.
The two were part of a crew and had a right to be in the pit area, but said no more about their roles, Johnson said.
There were no reports of any other injuries.
The raceway was hosting the California Sprint Car Civil War Series on the opening day of its season.
Steven Blakesley, the announcer calling the race from the stands, told The Associated Press the sprint cars were doing so-called "hot laps" about an hour before the race when a car driven by Chase Johnson, traveling at about 90 mph, couldn't make a turn.
"There must have been a mechanical problem," Blakesley said. "The car didn't slow down. "
Blakesley said the car ran through a gap between the track and pit row, then ran out of the view of the stands.
He said the next thing he was able to see was CPR being performed on two people, and later a body being covered and crime scene tape going up.
An outgoing message on the track's phone line said only that Saturday's race had been canceled, and a message left for a raceway spokesman was not immediately returned.
Sprint cars are small, high-powered cars that normally race on short dirt ovals. The races often serve as stepping stones for drivers seeking to get to NASCAR.
The race track fatalities come less than a month after a crash on the last lap of a race at Daytona International Speedway injured at least 30 fans Feb. 23. The victims were sprayed with large chunks of debris — including a tire — after a car careened into the fencing that is designed to protect the massive grandstands lining the track.
More Sports Headlines
Snohomish mixed martial artist returns to her first love Mariners beat Twins 4-3 in 11 innings Charles scores 29 points, Liberty beat Storm 78-62 Park wins Women's British Open, captures 4th different major Perry wins 2nd straight Champions Tour's 3M Championship Merritt shoots 67 to win Quicken Loans National by 3 shots Triple Crown winner American Pharoah wins $1.75 million Haskell Invitational Bills' Ryan names Incognito starting left guard
Our new comment system is not supported in IE 7. Please upgrade your browser here.