Here is one of my thoughts on this marker.
There is a very steep bank in the distance, This just happens to be the North bank of the Gunnisson River. The river (concealed by willows right at this place) is about 75 yards across at this point. the marker sits on the very North edge of the Uncompagre Plateau. This may be one of the key markers showing the beginning of the trail that cuts south across Colorado, Southern Utah, Northeastern New Mexico and into Arizona, bypassing Sana Fe by several hundred miles. We have since found several markers of prominence that are at least as large (and just as weird) as this along this edge about every 12 miles. There is a route up onto the plateau near each.and always there are more monuments leading Southwest, that start to converge around the "Gateway" area they come together as one solid trail just before Monticello Utah. There are trails coming South from Western Utah that converge into this trail on the other side of the valley after they cross the Colorado River.
I think that these are the markers that the Escalante Expedition missed by Staying too far North of the Gunnisson.
These are very much the Alpha markers that would have written us all a different history.
Your "KEY" may still unlock a door.