The Bureau of Land Management said that the ranger was patrolling the 50-mile race on Aug. 14 when a spectator flagged him down and reported the truck went flying into the crowd.
"The ranger immediately responded, and once at the scene, quickly assessed the situation, and called for emergency support," Jan Bedrosian, BLM deputy state director of external affairs, said in a statement.
With trucks flying by at speeds up to 100 mph, many spectators were mere feet from the desert course.
The tragedy has raised questions about the BLM's oversight of such events.
In an effort to step up enforcement following the crash, the BLM had eight employees, including three rangers, staff a motorcycle race in the same area last weekend.
The Associated Press contributed to this report.