First of all, I want to say I'm very happy that Laytonian is back! I also want to thank Believe09 and sarx for joining in and breathing new life into this thread.
For some reason, up until now, I didn't realize that Ruby Valley is 550 miles away from St. George; I guess I had just assumed it was a 2-3 hour drive, but 1100 miles round trip?! That, in my opinion, is a bit far to drive to just 'do some thinking' or even to visit a girl. That is like an 8 hour drive each way. Would Steven really go all that way to visit AN without even knowing if she was there? Was he in that general area for another reason? I find it more than coincidental this drive occurred only a couple of days before his disappearance.
As far as the cell phone pings go, my understanding is that in an urban area, if the closest cell tower is 'busy' with the pings of other phones, then your phone will be pinged off another tower in the area. For example, even though I'm in Greenwich Village, my cell phone could ping off a tower in the Bronx if it were a time of day when lots of people were using their cell phones/had them on. So it's definitely possible that LE is unable to precisely triangulate the last ping on Steven's cell phone, and that they are unable to determine exactly where he was when his phone last pinged.
Right now, though as Laytonian says all the theories have holes, I think suicide seems like the most logical explanation. My biggest problem with this theory, however, is the "HOW", and I haven't seen this discussed on this thread very much at all. If Steven walked out into the desert or up into the hills to commit suicide, how would he have done so? We haven't heard that Steven owned a gun or if he did that it is missing, and if he had recently bought one I'm sure there would be records. Did LE check on this, does anyone know? I seriously doubt Steven would have known where to get one on the black market, and he didn't have the money to buy one anyway. And other than a gun, how would he commit suicide? It could take days to submit to the elements, and it wasn't THAT cold, so I find this scenario unlikely. So other than the elements/gun, what do we have? Hanging? Overdose? Both of these seem unlikely to me as well. I'm sorry if this sounds morbid/graphic; I'm just trying to logically think through the suicide theory, and figure out the "HOW" in order to determine if this scenario is likely. The things that do point in this direction are the not answering calls from friends in recent days and that he didn't cash his grandmother's check or use his parents' money to pay his rent; if he had already decided he was going to commit suicide, he would have seen such expenditures as wasteful.
I'm just so frustrated, and want Steven to be found, wherever he is and whatever state he is in. Again, I want to thank Laytonian for coming back and all of the new posters for their new ideas and contributions. Thank you!