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

SCIGN USGS GPS Network - SGPS-San Gorgonio Pass 1 P.S.
Start: 29-Sep-1999
End: 19-Nov-2021
Hudnut, Kenneth, King, Nancy, Aspiotes, Aris G., Borsa, Adrian A., Determan, Daniel N., Galetzka, John E., Stark, Keith F., 2006, SCIGN USGS GPS Network - SGPS-San Gorgonio Pass 1 P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5DF6PGV