Interesting, I left the scanner searching those ranges . Here is what I found:
415.075 Repeats 166.375
415.475 Repeats 171.475
415.575 Repeats 171.475 (not a typo - diferent link to same VHF as above )
415.525 R "tanker base"
Had a second scanner scan the Joshua tree VHF and UHF link as well . Conditions might be bad right now as neither one broke the squelch all day. I have picked up the VHF beofre from my present location. My records show that 417.575 was/is either Lytle Creek to Rogers peak or Paxton hill to unknown tower. If memory serves, it was the old style tone burst type. Maybe they replaced it with microwave.
It looks like the BLM and the Forest Service, which use all the frequencies listed above, have not made the change yet. As the direction was just changed in January the next couple years will be a time of transition and hearing down links on 415 and 417 MHz will still be heard, but could change overnight.
It is interesting to see the air guard link on 415.525 still being used on the San Bernardino NF. This is a very common down link for air guard around California. Its use ended in my local area (Inyo NF) this last spring. It was a nice setup as the down link repeated the up link. I'm not sure why, but this feature has been dropped around here.
Having two or more UHF links for the same frequency would indicate that there is more than one remote base on the San Bernardino NF. I could guess that due to the topography of the Forest, one remote base might be somewhere on the San Jacinto Ranger District south of I-10 and one somewhere in the San Bernardino Mountains. I seem to recall that it is located on a peak in the area of Keller Peak. I have it marked on a map upstairs but getting up there is s big effort so I will leave it unnamed at this point. I might be cleared for putting weight on my left leg in two weeks and conclude the forced bed rest that I have been in since September 3rd.
The San Seavine to Rogers 417 MHz link was replaced with microwave some years ago. When traveling south to visit family I used to listen to this link all over the high desert, but it has been 5 years or more since I've done that. When I first became aware of the 417 link I was amazed that a UHF link could use a path from a peak near Lytle Creek to Rogers without an intervening hop. I was even more surprised to find out that microwave on this path was possible also. 417 MHz was/is used by the Dept. of Interior in many locations.
I think the reference to the "north entrance" must have referred to the entrance to Joshua Tree NP near the Park HQ/Visitor Center near the town of Joshua Tree off Highway 62, if I remember the number correctly. The south entrance that which is accessed off I-10.