While researching my giant-loop of a ride for this summer, from Ottawa south to the TAT, up the spine of the Rockies, and then back east via South Dakota Badlands and Michigan's Upper Peninsula, I ran across this route in ADVRider that's just too good to not share. Now to see how I can incorporate this into my return journey. GPXes are available through this link.
Those dunes are amazing! Did not know the glaciers left sand so deep in this area! Photo from the route creator's (Cannonshot's) photoessay.