Some of those indistinct trails are super hard to spot, unless they go around marshes (and there are often deer/hunter/orienteer trails around marshes). I get burned by them all the time, as I'm too trail dependent. Igor's QuickRoute is always a straight line to the next control, so he remains unphased by their presence or absence. I aspire to his contour reading.
I think the big radio telescope is still in use.
http://www.umich.edu/~lowbrows/history/peach-mount...The optical buildings look a little rough these days, but are still cool to go by.
http://www.umich.edu/~lowbrows/history/portage-lak...One quirk on Peach Mountain is that I've only found two proper ISOM boulders, but lots of black dots on the map where 0.3 m rocks lay. Don't count on them for nav! (They are great for course setting reference points though!) Pontiac Lake is the other map with rock piles mapped with the cairn symbol like Mill Lake was.