From the record
“Buck Mountain Lookout Tower is a groundhouse and fire lookout in the Coronado National Forest in Arizona, United States. The structure was designated as a National Historic Lookout on April 1, 2001, and was added to the National Register of Historic Places on December 14, 1987.”
Wikipedia article Buck Mountain Lookout Tower, CC BY-SA 4.0.
One of 140 National Register listings published here for Coconino County · listed in 1988 · category: Structure · built in 1939.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service