The fire started on July 4, according to the overview at InciWeb, and was monitored until July 16 when rapid growth prompted the deployment of firefighting resources.
Douglas County, home of the Pine Nut and Fish Springs horses, is now threatened but no evacuation orders have been issued.
This video from Storey County, a few miles to the north, suggests that the Virginia Range mustangs are also affected.
Western Horse Watchers Association 