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

Yellowstone Caldera GPS Network - OFWY-Old Faithful P.S.
Start: 20-Sep-1999
End: 17-Nov-2003
Smith, Robert B., 1999, Yellowstone Caldera GPS Network - OFWY-Old Faithful P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5DB803C