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

PBO GPS Network - P524-SquireCnynCS2007 P.S.
Start: 17-Jan-2007
End: 27-Jan-2009
UNAVCO Community, 2007, PBO GPS Network - P524-SquireCnynCS2007 P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5FF3QBN