(AP) – Investigators are still trying to determine the cause of a fire that destroyed thousands of hay bales in southwest Kansas.

The fire started May 28 near Moscow and was considered extinguished by June 5. But workers at Abengoa Bioenergy are still spreading the hay out to check for hot spots.

Officials say the blaze destroyed an estimated 38,000 hay bales, most owned by Abengoa. The company says workers will continue to spread the hay for the next few days. Once that’s done, cleanup will begin.

The Garden City Telegram reports the company has not yet determined value of the hay that was lost.

The Kansas Department of Emergency Management’s preliminary finding was that the fire was caused by lightning but that has not been confirmed.