An announcer at the track, Steven Blakesley, tells ABC News that driver Chase Johnson's car had apparent mechanical problems and did not make the corner at turn one, which resulted in him hitting the left wall and striking two people.
The race had not officially started yet; the crash took place during a practice run.
One of the victims is Johnson's 14-year-old cousin. The other, a 68-year-old man, owned a few cars in the race.
Blakesley also tells ABC News that the 30 teams entered in the race have donated their combined entrance fee of around $10,000 to the families of the victims.
The raceway was hosting the California Sprint Car Civil War Series on the opening day of its season.
An outgoing message on the track's phone line says only that Saturday's race has been canceled.
(The Associated Press contributed to this report)