This is the number one (read, only) immediate access locals trail in Great Falls--no more than 5-10 minutes from just about anywhere in town. There are no mountains and precious few trees, but the trail does offer some technical spots, especially if you know where to look. Follow the paved path East from the parking lot and immediately look left for the singletrack. Follow the ST east. After crossing a couple paved paths, the trail will briefly turn to doubletrack and back to singletrack. Then you plunge into Whitmore Ravine, cross the bridge at the bottom and get your first taste of work as you climb the other side. After exiting the ravine, trails that branch off to the left will generally give you the most technical challenge while trails that go straight or to the right are more smooth prairie cruising. There are a few "secret" trail that branch off left--take them only if you are comfortable with technical obstacles and scary exposure. It's about three miles to the Rainbow Dam overlook, a good turnaround point for most. Or you can go another three miles or so to the Ryan Dam overlook. It's possible to continue past Ryan Dam, but then, you're really on your own in the middle of nowhere. Beware--the return trip is upstream, so there's a little more climbing than on the way out. More importantly, it's almost always windy here, and the return trip is straight into that wind. On certain summer weekends, the top of Rainbow Dam is open so you may cross and hit the dirt road on the other side of the river which then leads to the more scenic and consistantly entertaining North Shore Trail.
In Great Falls, follow River Road to the turnoff to the Lewis and Clark Interpretive Center. Go past the center, under a bridge, and up a hill. Pull into the second parking lot on the left as you climb the hill.
http://www.singletracks.com/item.php?c=1&i=2412