From the record
“Fort Logan and Blockhouse is a site on the National Register of Historic Places located near White Sulphur Springs, Montana. It was added to the Register on October 6, 1970.”
Wikipedia article Fort Logan and Blockhouse, CC BY-SA 4.0.
One of 6 National Register listings published here for Meagher County · listed in 1970 · category: Site.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service