Six or seven cars were on the track Saturday night when the out of control car ran into the two victims, who were standing side-by-side, Yuba County Sheriff's Capt. Ron Johnson said. He said the two were affiliated with one of the cars or drivers but did not yet know how.
Neither the 17-year-old driver nor anyone else was injured, he said.
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, the officer told The Associated Press.
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, said 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, hit an empty golf-style cart then ran out of the view of the stands, where fans were mostly silent and left to speculation about what was happening.
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. The names of the victims weren't immediately available.
The bio on Chase Johnson's website said he's a senior at Petaluma High School north of San Francisco and is a fourth generation race car driver.
Blakesley said Chase Johnson had been driving for two years already, and many on the sprint car circuit, seen as a stepping stone to higher levels like NASCAR, began as young as 15 as Johnson did.
He said others on the circuit, where small, high-powered cars race on short dirt ovals, were older drivers whose careers had peaked earlier.
The Sheriff's Department and California Highway Patrol were investigating to determine the cause of the crash, Ron Johnson said. The Sheriff's Department also serves as the county's coroner and would determine the identities and official cause of death for the two victims, he said.
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.
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.
At another NASCAR race in 2009 at Talladega, the crowd was showered with debris and seven fans were injured when a car sailed upside-down into the front-stretch fence on a furious dash to the finish line, showering the stands with debris. Seven fans sustained minor injuries. And in 2010 at a National Hot Rod Association event in Chandler, Ariz., a woman was killed by a tire that flew off a crashing dragster at Firebird International Raceway.
Associated Press Writer Andrew Dalton contributed to this report from Los Angeles.