My thoughts:
Drinking beer.
Many of us know what effect beer has, in essense: beer in, p@@ out. Maybe BT needed a bathroom break, stopped along the way, maybe next to or under desert brush she encountered a poisonous snake or other?
Hiker Curiosity.
While hiking, one may encounter interesting elements along the way, such as unusual rock formations or desert plants. Maybe BT climbed a rock formation to get a better view of the surrounding area and she slipped and fell between separations in the formation?
I suspect BT couldn't have traveled far from where she was last seen, I'd expect LE to have concentrated their search in the immediate area, as opposed to spreading resources in a larger circumference fan-out. If not, why not?
Unfortunately, it's a desert, 100 degree temps, no water or other supplies... I'm willing to bet BT is found within 500 yards of where she was last seen.
Of course, there is that always-lingering possibility this case turns out to be a spouse-on-spouse crime but as of yet, the only 'indication' of that is RT's admission that he submitted to a polygraph and LE claimed the result indicated he was being 'deceptive'.
How often did the couple go hiking? In the desert? Elsewhere? Did RT always take photographs on their hikes? Did the couple hike for the scenery, to exercise, both? Why was that location chosen?
RT claimed to have stopped to "take a photograph." How many times did he stop to take a photograph during that two-mile hike? Two? Twenty? Two-hundred? What was it that he last photographed? Are the photos consistent as to subject, interest? What if he stopped to take only one photograph?