If you hike in the Sandia Mountains, you may have encountered a tree with a small aluminum disk at eye height. The disk provides an approximate germination date ("GD") and a contemporary event in world history. For example, the disk shown above occurs on the pinyon pine shown below. The pinyon is on the crest of the Sandias and you're likely to pass it if you hike from Crest House to North Sandia Peak.
If you go to the Hikes tab on this web site and scroll down, you'll encounter a downloadable PDF that lists all of the trees and their locations. I found the on this web page.