The following information obtained from UNAVCO's online DOI system:
(https://www.unavco.org/data/doi/search/search.html)

Southwest Montana GPS Network - SHPM-Sheep Mountain P.S.
Start: 24-Sep-2011
End: 01-Sep-2019
Bendick, Rebecca, 2011, Southwest Montana GPS Network - SHPM-Sheep Mountain P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5SB43P4