Judy Barnes, founder of the nonprofit, was house-sitting in Santa Fe when the incident occurred, according to a story by KRQE News of Albuquerque, NM.
Her home was destroyed, along with $5,000 worth of horse supplies.
Investigators have not determined the cause.
Barnes has been looking after the free-roaming horses of Wild Horse Mesa for nearly twenty years.
RELATED: Wild Horse Mesa Confirmed.