I go to school in Bozeman and I was just up Brackett Creek last weekend. Three miles past Bridger, there is a parking area to your right and the trail heads in on the left. My friend and I didn't unload here. We kept going up the highway another few miles, to the very top, and parked along side the road before it began dropping down the other side. The trail starts right there. You ride packed trail for 4-5 miles before it opens up into a bunch of litte bowls and play areas. I'm almost positive this is Brackett Creek, it was my first time in there, but I talked to a guy who rides up there all the time and he told me that it's the Brackett Creek trail. Hope this helps. Good luck.
