More about the search
I started working on the Lessons Learned post this evening, and in order to talk about that topic I think we need to share some more details of the area where Nancy and George were, and how we approached searching it. So this post is an overview of that topic.
Where they were
Now that we know how Nancy and George's wilderness walkabout ended, we can take a step back and think about where they may have been. The map below has blue dots at the the four places they were seen, and a red line along Quartz Hill Road. Nancy has been to Vipond many times (usually with no off-leash time), and Quartz Hill Road is the only route we have ever taken to get there.

We believed Sunday night, and continued to believe all week long, that although they could have strayed off side roads in a few places, they were mostly likely hanging out somewhere along Quartz Hill Road. It's a road Nancy knows well, and in the first few hours we know that they walked 2.5 miles down that road to a cabin where they were sighted.
So we searched Quartz Hill Road more than any other place. I drove the length of it as soon as I arrived to search every morning, and drove it in the evening at the end of every day of searching, as well as multiple times in between. Others drove it, too, especially later in the week, either because they were helping with the search or simply because it's the only way in to that area.
Leaving Quartz Hill Road
Most of the terrain in this area is too steep and rough for dogs to travel on. This reduced the number of areas that needed to be searched. It's still a vast and remote area, but the number of places the dogs could make it to was limited. Generally speaking, there are five main ways that Nancy and George could have left Quartz Hill Road to travel to other areas, and these are shown in orange on the map below.

I'll briefly describe how we ruled out each of these areas.
Starting with the bottom (most southerly) one first, we have Canyon Creek. A dangerously exposed road leads from the high Vipond meadows down along a cliff to the Canyon Creek charcoal kilns 800 feet below, and that area below the cliff also has a campground, some ranches, and a rental cabin. I drove to the top of the cliff several times during the week, and others – including our friend Ron on Monday, and local expert Keith on Tuesday – searched the area below the cliff.
I was doubtful that Nancy and George would head to Canyon Creek. It's nearly 10 miles beyond where they had been spotted, and the last few miles have nothing to attract them, just a dry dusty road. But we searched that area throughout the week, just in case.
Next is Keystone Triangle Gulch, which is a rough overgrown forest service road that leads down to a dumpster along Highway 43. Some dogs that have gone missing in this area in recent years have ended up at that dumpster, presumably attracted by the smell. So it seemed worth searching.
Rodger and I searched the entire length of Keystone Triangle Gulch on Monday. It was a frightening experience, so much so that I forgot to take any photos because we were constantly in the mode of trying to carefully traverse steep and rough terrain with cliffs and other dangers nearby. We broke off the truck's kayak rack on an overhanging tree on this road, and we also had to move various downed trees and rocks in the road, and some places were so narrow that we scratched both sides of my truck.
Isaac and I came back to the dumpster below Keystone Triangle Gulch on Thursday, and drove up the road until we could get no farther. I was planning to hike the whole road on foot over the weekend if we didn't find them by then, because there was a pond halfway down that seemed like a place they might stay if they found it.
Near Keystone Triangle Gulch is Knoby Peak Road, which climbs a few hundred feet before traversing a ridge above Quartz Hill Road. Isaac and I drove the length of it on Tuesday, but didn't find Nancy and George. There were many muddy areas and we saw no dog tracks in them, so we were pretty sure they hadn't gone up this road.
Echo Gulch is the only route up out of the lower several miles of the Quartz Hill Road valley. I woke up at 3AM on Tuesday remembering it, a forest service road heading off to the side halfway up to Vipond. A few hours later, Isaac and I discovered that the forest service has put up a huge berm of dirt and downed trees to block access to it for motorized vehicles, to preserve elk habitat. So we had to search that one on foot. After a mile or so, the road/trail all but disappeared under fallen, so we were pretty sure they hadn't headed up that route.

Finally, there's Addson Creek, a trail that leads downhill to the west from the Vipond area, connecting to a logging road that eventually crosses the Wise River to reach the Pioneer Mountains Scenic Byway. Isaac and I searched this area Friday morning, driving up from Wise River as far as we could. The Pioneer Mountains Scenic Byway happened to open for the season that same day, May 15, so I decided that we didn't need to search this area any further because there would be people down there around the town of Wise River who would see them if they came down that route from Vipond.
Having thoroughly searched all of the routes leading away from Quartz Hill Road by Friday, I became convinced that Nancy and George must still be up around the Vipond meadows. So I called Eric the drone guy in Bozeman, and asked if he could meet me up there to search all of the meadow area again, this time in daylight instead of a thermal search. He said he could meet me over in Divide (a nearby town along I-15) at 6PM.
I was waiting for Eric in Divide when Megan contacted me to say that Nancy and George had been found. If they hadn't been found by Frank, Jess, and Sam, I'm pretty sure Eric and I would have found them an hour later, because we were planning to search that same area with his drone. Frank had spotted them out in the open along the road, where we would have easily seen them.
Where were they all week?
Now that they're safely home, we – and everyone else who followed their story – can't help wondering where were they all week? I drove past the spot where they were found many times during the week, often while calling their names, and others drove past that spot, too. Why didn't any of us see them?
Based on the details of our searches and where they were found, and the details of what happened in the first few hours of their adventure, as well as discussions with people who know the area well, I have a theory. We'll never know whether this is right or wrong, but for what it's worth I'm going to outline below what I think happened last week.

Sunday evening is key. That was the first few hours after they went missing, when Megan and I were searching up around the Vipond meadow and then we got a text from the women who had spotted them at a cabin along Quartz Hill Road.

When Megan, Isaac, and I drove the 2.4 miles from the Vipond meadow down to the cabin, we never saw Nancy and George along the way. I think that's most likely because they were headed back up to the meadow, but took a more direct route through the trees and snowdrifts that avoided the road.
After we arrived at the cabin, Megan walked down Quartz Hill Road calling for them, while Isaac and I drove all the way down to Highway 43 near the town of Dewey and then came back up the road slowly, calling for Nancy and George. When we got back to Megan coming down the road, neither of us has heard or see anything. I think this is because Nancy and George were back up at the meadow at this time.
We searched the road two more times, and then it was dark so I took Megan and Isaac back to Butte and then returned to search on my own. I drove through the meadow around midnight, honking and calling for Nancy and George, but never got a response. I think they may have been inside that dense forest at this time, having fun and ignoring me, just as they'd been ignoring me and Megan at the same spot a few hours earlier in the afternoon.
During the week, I think they hung around inside that forest, eventually finding the pond on the south side of it, where they could get plenty of fresh water to drink. I think they probably stayed inside the forest most of the time, because otherwise I and others would have seen them from Quartz Hill Road.
On Thursday night, Eric the drone operator searched that forest methodically with his thermal drone. He never spotted Nancy and George, but he did spot many elk in the trees. He mentioned that it's possible to miss a dog if it's right next to a big downed tree or something like that which could block its thermal radiation. For example, if the drone is slightly south of a dog and they're laying on the north side of a log or a boulder, we could miss them. I think that's probably why we didn't see them on Thursday night.
An interesting detail of that search: at one point, we spotted with the infrared thermal drone several elk running through those trees. Eric thought it was strange for elk to be running through trees at night, but we couldn't find anything they were running away from. Were they running away from a sighting of Nancy and George? Seems possible.
My theory in full: Nancy and George returned to that forest on Sunday evening, the same forest they had run into with Isaac when they were first off-leash, and then they spent the next few days in and around that forest, eating elk poop and vegetation while drinking at the nearby pond.
I'm interested to see whether Nancy will show me any further details of what they were doing. So I'm planning to get back up there soon with just her (on-leash, of course), and walk around that pond and into the forest to see whether she'll lead me to any particular location. More to come on that when we get the chance.