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

Geopentech GPS Network - VTOR-Vista_TwinCA2012 P.S.
Start: 15-Jun-2012
End: 14-Nov-2022
Walls, Chris, 2012, Geopentech GPS Network - VTOR-Vista_TwinCA2012 P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T59C6VJ6