Here is a very nice airmail label issued by National Parks Airways Inc. USA.
National Parks Airways was an airline operating in the US States of Idaho, Montana, and Utah in the 1920s and 1930s. Founded in 1927 by Alfred Frank, it began service with a pair of Stearman C3MB's. Air Mail was the first cargo; passengers came later. (wikipedia)
Year: 1931, Gummed. Günter Mair's catalogue no: - USA-B-205, imperforated, triangular shape, black/red/grey-blue/white, 4****