There is plenty of parking at the Alkali Trailhead. The Centennial Trail will start across the road from the parking area. Following the trail will take you under I-90 and across an open field before getting into the shade of the pines. You can do the loop either direction. There is a bit of a climb either way although the switchbacks keep it from being to steep. Finding the trail is a bit easier going clockwise in my opinion. To do this you will pass the first intersection with the Sturgis Trail System around mile 1.5 and continue on Centennial to the second intersection around mile 4.5. You will reach the dams at just under 8 miles. This is a perfect place to stop and have a snack and enjoy the sounds of running water. You will cross the dam and then head to the right to continue on the loop. Along the way, you will have views of Bear Butte, the city of Sturgis and the Black Hills. Overall, the trail is a nice rolling single track perfect for hikers or mountain bikers.