From the record
“Michael's Mission is an Episcopal church mission established about 1887 in Fremont County, Wyoming to minister to the Arapaho and Shoshone of the Wind River Indian Reservation. It was founded by Reverend John Roberts with the permission of Shoshone Chief Washakie.”
Wikipedia article St. Michael's Mission (Ethete, Wyoming), CC BY-SA 4.0.
One of 31 National Register listings published here for Fremont County · listed in 1971 · category: Building.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service · the Wikipedia article

