YOSEMITE NATIONAL PARK, Calif. — Investigators have learned that sparks from a vehicle at the edge of Yosemite National Park caused a wildfire that led to the death of a firefighting air-tanker pilot.

Meanwhile, another series of northern California blazes that destroyed six homes was threatening hundreds more near a major highway.

Fire investigators said Thursday that the blaze near Yosemite broke out because of hot metal fragments from a vehicle creating sparks, Yosemite officials said in a statement.

Investigators had not determined what type of vehicle or what part may have caused the sparks, saying it could be the result of several things such as trailer safety chains dragging on the pavement, vehicle brake parts generating a spark or other sources.

They didn’t immediately say what evidence led them to the cause of the fire that had burned 245 acres and was 10 percent contained.

Within a few hours of the blaze breaking out Tuesday, a state fire air tanker crashed into a canyon wall, killing 62-year-old pilot Geoffrey “Craig” Hunt of San Jose.

CalFire’s fleet of 22 tankers remained grounded while the cause of the crash was investigated.