The incident started on June 7 in Glen Canyon National Recreation Area according to a news release dated June 23 by NPS.
The horses were trapped on a beach in Navajo Canyon due to rising lake elevations and with food running out, the Park Service loaded them into a horse trailer on a boat and handed them off to Best Friends Animal Sanctuary in Kanab, UT.
NPS does not acknowledge the horses in its discussion of mammals in GCNRA, probably because it considers them to be non-native/invasive animals.
The National Data Viewer puts Navajo Canyon in Arizona near the Utah state line.
Western Horse Watchers Association 