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

PBO GPS Network - P721-YNP_NEEnt_MT2005 P.S.
Start: 30-Sep-2005
End: 25-Sep-2022
UNAVCO Community, 2005, PBO GPS Network - P721-YNP_NEEnt_MT2005 P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5PG1PPG