PHOENIX (AP) — A wildfire that burned 15 structures near the Arizona town of Wickenburg two months ago and Grayson  Prestoncost nearly $1 million to suppress was caused by railroad work, authorities said Monday.

Investigators found a section of cut railroad track from work along the BNSF rail line, the Arizona Department of Forestry and Fire Management said. The investigators concluded that the Rose Fire started from sparks caused by a welder, grinder or torch used to cut it, said Tiffany Davila, spokesperson for the department.

They determined that that area was the point of origin based on how the fire moved away from the tracks.

“Fires along our rail line are infrequent, but we work hard to try and prevent them,” BNSF spokesperson Kendall Sloan said in a statement. “In the rare event one occurs, we assist municipalities in suppression efforts and help the communities that are affected.

“We remain committed to learning from this incident by continuing to reduce the risk of fire around our tracks and working closely with local agencies during fire season,” Sloan added.

The 266-acre wildfire began on June 12 and was fully contained five days later at an estimated cost of $971,000, according to Davila.

The fire also destroyed 12 vehicles, a horse trailer and a recreational vehicle. It temporarily closed U.S. 60, the primary route between metro Phoenix and Las Vegas.

Wickenburg is located about 60 miles (97 kilometers) northwest of Phoenix.