These are unusual drives at night... to go to the River Road means going through at least one in-country checkpoint, possibly two. A Mustang is unsuitable for any off-the-road ventures. I've been thinking that the drive Wednesday night could have been to check on something done earlier Wednesday.
Do they record your name or vehicle info when you go through those checkpoints? IF RF rode around in a vehicle in an area that required going through checkpoints I wonder if he could have done it to establish an alibi or throw off any future investigation?
River Road is possible to get to without crossing the checkpoint. However, the routes are pretty well patrolled by CPB and ranch owners. That car would have been stopped or noticed if seen on any side roads, too risky. And it would take a few hours roundtrip of dodging giant jackrabbits lunging onto the road every 1/4 mile...a guy who loves his fancy car is not doing it. The mustang cruise was probably just a local cruise as his friend stated. *btw- "local" includes a solid 30 mile radius here. That doesn't mean the friend was unaware that he was chauffeuring RF around the area to check on things.
There is a checkpoint in Marfa that RF would have gone through when driving his mother to Presidio; and he would have traveled River Road (FM 170) as well. If they are searching those areas based on RF's cell phone pings, it seems to stem from that trip.
Returning from Presidio, there is Pinto Canyon Road (FM 2810). It is narrow, winding and often rutted out and impassable. There are plenty of steep cliffs and places to dispose of anything. There is no checkpoint and little to no cell service, but there are webcams and road sensors. Chances of being spotted by CBP and/or illegal immigrants hiding in the bushes make it pretty high risk.
If RF waited a day or so to transport a deceased body in a small SUV with mama riding shotgun and disposed of it on the return trip... Then either mama knows or he immaculately eliminated evidence.
All that (and my wordy posts prior) being said... if RF is guilty of her disappearance, she must be somewhere close to home. LE either has no real leads or they're bluffing. After an 11 day massive investigation, I fear no leads. As a woman in this town, that's really terrifying me.