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

SCIGN USGS GPS Network - MILK-Millikan Library Caltech P.S.
Start: 24-Jul-2013
End: 14-Nov-2022
Hudnut, Kenneth, Determan, Daniel N., Aspiotes, Aris G., 2015, SCIGN USGS GPS Network - MILK-Millikan Library Caltech P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5G73C08