Wow, I just made the world's ugliest screen shot. I am so proud.
I just switched to a new computer since my old one crapped out and now nothing is where I like it, so bear with me. But here's a tentative idea of the kind of thing I have in mind. I've pretty much decided to go in from the NE and try and fill in some gaps in the area. I will probably also range much further west towards the odor location, following another "fill in" type contour along the rim of Smith Water.
This screen grab gives a rough idea of my thoughts. This might be the way we approach. There's nothing pretty or pleasant about it - will be a lot of on-a-slope walking. That's what adjustable hiking poles, mid-length boots and a careful step are for.
This screen grab is from Google Earth. I laid in one of OtherHand's cell coverage views, the one that is "clearest", to give an idea of where we're looking. Smith Water runs down the screen from left middle towards the top center. Quail Wash comes down where the black tracks are. The baby blue is the search tracks from JT45. The little red squiggle is the kind of thing we might do. You'll notice how we're going up, and then down. I may save investigating that green gully where we suspect water might be for the return trip instead - in fact, I probably will. I just want to give a rough idea of what's floating around in my head right now. I'm considering a dip or two towards Smith Water, but - having been out in Joshua Tree recently, I have looked hard at the terrain. If you're injured to the point where you cannot easily walk, distance is hard to come by. An experiment if you wonder how hard: sit down on your lawn. Scoot along backwards on your butt, dragging a leg. See how tiring it is. I tried it. I've forgotten how tough it is to drag yourself over the ground. Walking with my bruised leg, I was reminded of how mentally taxing it is to force yourself into pain with every step. Imagine having real, debilitating pain from a joint injury. So I wonder if you're going to want to give up altitude when you've made it all the way to this spot. Bill sent out a cell ping. He was hoping to call in help. He may have been hoping to be seen from the air. Maybe he was up in this cell coverage area on Sunday. Would he have lost altitude in a last ditch effort? Would he have stayed in the area? I don't know, obviously. I hope by filling in a few gaps and by descending toward that vegetation spot, I might answer some of these questions for us by a process of elimination.
I'll take the GPS tracks with me and try to cover mostly new ground. I have to balance searching on this trip with make sure my spouse will ever go on another trip with me

but I am hopeful of adding to the body of knowledge we have. I have a very patient, detail-oriented personality. I can spend days covering every inch of ground in a detailed search pattern for you. My spouse, on the other hand, has an "entertain me now" personality. We'll see how this pans out.
Hikin_Jim - your idea of a steep north face is a great thought! A north face would make cell coverage for that ping that much more likely. I am going to spend some time looking for north-facing boulders on Google satellite view, and also keep it in mind during my search.
Thank you, also, for the recommendation on some binoculars. I will try to head down to a store and see if I can find something. I kind of live in a backwater, so it is hard to find good stuff in regular stores, but we'll see.
Any thoughts, advice, etc, still appreciated.
