From the record
“The N-Bar Ranch, near Grass Range, Montana, dates from the 1880s. It was listed on the National Register of Historic Places in 1991; the listing included 13 contributing buildings.”
Wikipedia article N-Bar Ranch, CC BY-SA 4.0.
One of 48 National Register listings published here for Fergus County · listed in 1991 · category: Building · built in 1885.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service