Actually no. I don't believe they had to replace anything at all.
In fact, any land route, other than one across a constantly shifting landscape, could be easily plotted and followed by using natural landmarks alone, or supplemented with a few more or less natural but recognizable features at key points along the way. These would not have to be large or require a great deal of manpower to construct or modify in order to serve the desired purpose. The only "map" needed, might be as simple as a list of these landmarks, perhaps scrambled as they are on the Latin Heart.
Your "road sign" analogy is partly correct however, and I believe there was a system of common "road signs" used (analogous to a significant biblical revelation) from the beginning of the trail at the Gila, to the area at the end of the trail. This area is defined by three such markers, with a fourth within the borders, which may very well turn out to be a bullseye. If one or even a few at random were to be lost, it would only add a slight degree of difficulty to following the trail, since as a backup, one would have the descriptive notation on the "map" itself to fall back on.
While I doubt earthquakes were a primary concern, I do believe any rational person would recognize the folly of constructing large markers of any kind. These would only draw the attention of the curious and perhaps destructive inhabitants of any given area. Any invasion of their territory, as Springfield has pointed out, especially of "thousands of people" making massive alterations to the landscape as you claim, would have been a major disruption to their way of life. History has shown how they dealt with both the intruder and his architecture in similar cases.
Unfortunately, I am at present too far north for any get together with you and Tom. Perhaps later in the spring, if I can make it back down.
Regards:SH.