Mystery Medallion '17'

This is a medallion, one of hundreds affixed to trees, mostly old Ponderosa pines, and a few other types, located in the forest between the towns of Tijeras and Cedar Crest, New Mexico. The medallions indicate the age of the trees, taken from core samples, as indicated by G.D. (germination date), as well as an event from that year in history. Occasionally a tree was dated after it's death, and includes the D.D. (date of death) as well.
This work was undertaken by a private citizen, unaffiliated with any public or government organization. Not only was the work accomplished in secret, but the name of the diligent scientist who accomplished all this is unknown.
The U.S. Forest Service denies any knowledge of the medallions. Seeing them requires hiking in about 5 miles.