Forest Service investigators determined the Calf Canyon Fire was caused by a “burn pile” of branches that the agency thought was out but reignited on April 19, the Santa Fe National Forest said in a statement.

That blaze on April 22 merged with the Hermits Peak Fire, which the USFS started with a controlled burn that went out of control on April 6, the agency previously reported.

The combined blaze has so far torched over 312,320 acres(126,319 hectares) of mountain forests and valleys, an area approaching the size of greater London, and destroyed hundreds of homes.

“The pain and suffering of New Mexicans caused by the actions of the U.S. Forest Service – an agency that is intended to be a steward of our lands – is unfathomable,” New Mexico Governor Michelle Lujan Grisham said in a statement.