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A while ago I noticed this formation on satellite maps. Not only are they straight lines a mile on a side, they're oriented exactly with the cardinal directions. The lines are pretty clearly vegetation, but there's no mention of what it might be on the EBMUD trail map. So I ran back in there with the annotated trail map and a GPS. Those lines are rows eucalyptus trees - tall old ones - planted exactly aligned with the cardinal directions, which is not easy considering the rather robust relief of the land back there. Ramage Peak Trail goes right through it - from inside, if you weren't looking for it, you might not notice the straight lines of trees since it's pretty big. There is evidence of cattle terracing inside on both sides of the summer-dry creek bed running up the middle.
So what is this? It wouldn't keep cattle in because at their bases the trees aren't close enough together, and yes I know that often eucalyptus is planted as windbreaks, but then it would be one stand, right next to a house or field with fragile soil or crops. Any theories? Yes, I know I could just call EBMUD and they'd probably tell me but that would spoil the fun.