From the record
“Canyon de Chelly National Monument was established on April 1, 1931, as a unit of the National Park Service. Located in northeastern Arizona, it is within the boundaries of the Navajo Nation and lies in the Four Corners region.”
Wikipedia article Canyon de Chelly National Monument, CC BY-SA 4.0.
One of 24 National Register listings published here for Apache County · listed in 1970 · category: District · built in 1931.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service