You can core a tree to determine its age. Aspens grow fast, but seldom live more than 150 years. Most die off after 80-100 years. 2020-150=1870. Add another 25 years required for a sapling to grow big enough to carve all this stuff and you get about 1895, best case scenario. Of course, if this tree was one in a million, say it's 200 years old. That puts you about 1850. The Spanish era? No. Mexican? Likely not. It looks like the map is about the same age as the other graffiti on the tree, maybe 20 years. Believe what suits you.