Unlike the South unit of TRNP, there is no trail allowing mikes to go around the North unit. So you're left with a short MDH out-and-back which can not be connected to the rest of the MDH, of you can head out and make the turn on to the Long's X trail to form a nice loop. Get a copy of the Little Missouri National Grasslands map. Unlike the Medora end, this end of the MDH is VERY remote and almose never visited, so you'll have the place all to yourself. Mileage for the loop is about 12. You can crank that up to about 16 if you include the out-and-back ont he MDH to the park boundary.
From Watford City, head South. After the entrance to the North Unit of the Teddy Roosevelt National Park, cross the river and make a right turn into the CCC Campground. Pick up the Maah Daah Hey Trail at the west end of the campground.
http://www.singletracks.com/item.php?c=1&i=2322