A simple reason ~ you didn’t follow the route of the Santa Fe Trail ~ it’s located along the rivers ~ this is above the flood path (if there ever is one) just like surveyors might have placed a stone marker.
If you mean have I hiked the entire Santa Fe Trail, no I haven’t but I have been on many different parts of the trail. Also I have visited many fabulous Indian sites, both inhabited and abandoned in NM. I have never even seen a sign or marker or indication on a NM map about this stone.
My next trip to NM I am going to look this up!