When a golfer trying to hit a ball out of the rough struck a rock with his club, it started a fire which burned across 12 acres in California.
The fire spread across the rough and reached the brushy hillside next to the Shady Canyon golf course in Irvine on August 28.
About 150 fire fighters battled the blaze.
Orange County Fire Authority Capt Greg McKeown told BBC News that investigators were able to determine the cause of the fire by interviewing people at the golf course.
"Personally, I've never responded to that call before," he said.
There were no charges filed against the golfer.
Fires have been a major problem in southern California recently because of dry conditions.