I monitored the control channel data about a month ago on a visit to the area and it still only showed two sites active and no affiliations. But apparently they have been busy with this system build-out.
I suspect this is a Department of the Interior system that will support the Bureau of Reclamation and other DOI activities in the Lower Colorado region.
Although it is listed as "Clark, NV", I am certain that site 112 is at or near the Hoover Dam area, as I get close-call hits on that control channel when I am at the dam.
Here is what is showing at Radio Reference:
2-013 Site 13 Riverside, CA 172.1125
2-061 Site 61 Yuma, AZ 172.650
2-065 Site 65 172.6502
2-075 Site 75 172.1375
2-122 Site 112 Clark, NV 172.1125