From the record
“The Rainbow Conoco at 400 Main St. in Shelby, Montana, also known as Joe's, was built in 1936. It was listed on the National Register of Historic Places in 1994.”
Wikipedia article Rainbow Conoco, CC BY-SA 4.0.
One of 6 National Register listings published here for Toole County · listed in 1994 · category: Building · built in 1936.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service