It turns out that in 1878, when they surveyed the boundaries of Utah-Colorado-New Mexico and Arizona, they adjusted the spot where the four territories met (unique in the U.S.) so that the location would be easier to get to.
It should have been at the confluence of 37ºN and 109ºW. That’s about 2½ miles east and slightly north of where the Four Corners Monument is located today near 36°59′56″N and 109°02′43″W.
The states and Congress ultimately recognized the error, but accepted it, and the Four Corners Monument marks the official boundary. You don’t have to go back to take photos all over again.
The present monument is on sovereign Navajo Nation land. The actual confluence of 37ºN and 109ºW is also on Indian land, the Ute Mountain Reservation.