What about site 12?
I looked at the FCC info for FRN 0001586155 and found that there's substantial overlap in the frequencies between Red Mountain, Upper Black Mountain and the Rio.
FWIW:
These are largely common with Upper Black Mtn and the Rio, but I didn't see them being used:
WPQF978
0851.1000
0851.3750
0851.4625
0851.6250
0851.9250
0852.1625
0852.2750
0852.9750
0853.5000
0853.8250
===
WNQU894
Site 12 Red Mtn along with Black, Rio and the 4 sites under WQRK432
0851.0500
0851.2500
0851.4000
0851.5500
0851.6500
0851.9000
0852.2500
0852.4000
0852.6125
0852.9125
0853.1875
0853.4000
0853.8250
0853.9000
0854.3125
0854.4125
0854.7125
0855.7125
0856.2125
0857.1125
=======
Also on the above license:
Shows up on Unitrunker as P25 Site 001-021
0856.7125
0857.7625
0859.2625
0859.9375
=======
P25 Site 001-22
0856.4375
0856.7625
0857.4875
0858.7625
0859.4625
0859.9375 (yep, shows up on both sites)
======
This leaves these unused on that license.
0856.2625
0860.2625
0860.4875
0860.4875
0860.9375