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

PBO GPS Network - P442-DarringtonWA2006 P.S.
Start: 22-Mar-2006
End: 26-May-2020
UNAVCO Community, 2006, PBO GPS Network - P442-DarringtonWA2006 P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T56T0JMN