Eric Charette posted the route:
Original post on ericcharette.blogspot.com/2012/05/greenstone-ridge-trail-fkt.html
The Greenstone Ridge forms the geologic backbone of Isle Royale, which is one of America's least visited National Parks. The only way to get to the island is either by air or by sea as it is 90km away from the shores of Upper Michigan and 35km away from Grand Portage, Minnesota. The GRT traverses this ridgeline for 40.1 miles along the entire length of Isle Royale from the western terminus at the intersection of the Minong Ridge Trail (0.3 miles away from Washington Creek Campground) to the eastern terminus at the intersection of the Lookout Louise trail.
There are many reports of a park ranger from Amygdaloid (small island off of Isle Royale) who ran from Rock Harbor to Windigo in 2008 (documented in the personal log book of George Hite of www.eagleharborweb.net/ ) but did not traverse along the entire length of the GRT, but instead ran from Rock Harbor Lodge to the Windigo Campground. Apparently the ranger also ran back to Rock Harbor on the second day, which is a tremendous feat! There is also a claim posted on the BackPacker.com website www.backpacker.com/october-2010-50-mile-thru-hikes-greenstone-ridge-mn/destinations/14780 of "bstearns" running the GRT in 10 hours and 12 minutes. There are no other details of this report and while the aforementioned rules are mostly guidelines and since there is not sufficient information about this report, I can not validate the time. I have spoken with the National Park Service, several authors of books on Isle Royale, and numerous people on isleroyaleforums.com/ and no one can substantiate any faster times for the entire GRT.
VARIATION UPDATE September 2021
The original route posted above is for the GR Trail only. This is impractical, as one must hike to reach both ends of this trail, and the east end also requires a boat. FKT Guidelines now state routes must Start and Finish at accessible trailheads (except for summit finishes on mountains). Therefore, a new Variation has been established: "Greenstone Ridge dock to dock". This is the most logical and practical way of traversing the Greenstone Ridge, and should be considered the Standard Route going forward. Mileage, Distance, and GPX file are now shown for this Variation.
"Dock to dock" starts at the main ferry dock at either end (the exact location of which everyone knows, since unless they took a seaplane they arrived at one of these two docks), and goes in either direction to the dock on the other end. Simple. This means the last 4.8 miles on the east end of the Greenstone Ridge is not done; rather one uses the Mount Franklin and Tobin Harbor Trails going in or out of Rock Harbor.
Always stay on the trail, note that although one is literally surrounded by water there isn't much on the Ridge, and there is basically no cellphone service, so be careful.
This is the Strava Segment this GPX file was taken from: https://www.strava.com/segments/29192565
This is the Strava Segment that is slightly different (shorter), with 6 times on it, including a fast 8:06:34
The first FKT posted to this site should be faster than 10 hours for Men (anything for Female).
On Saturday, August 13, 2022, Erica Brewis and Abigail Cook will make their first ever attempt at an FKT, 40+ mile run, and possible (probable) wolf encounter. Erica and Abigail aim to complete the Greenstone Ridge dock to dock route, beginning at Windigo and ending at the Greenstone Grill at Rock Harbor for bottomless french fries. We look forward to sharing updates upon our return!