Keep in mind that this is a long wilderness hiking trail, so don't forget to pack enough supplies. Mill Creek Trail is 29.4 miles long; it's longer than many great outdoors trails. Some parts of Mill Creek Trail are much higher up than other parts of the great outdoors trail which of course means you need to be prepared for different conditions on different parts of the great outdoors trail. This great outdoors trail has only one trailhead, so you'll be backcountry hiking it in and back out. The total elevation difference for Mill Creek Trail is 5,463 feet, and that is higher than average. Of course, this is an overnight trek, 4.5 days normally, so it's a tremendous thing if your backpack is big enough to do the job.