Peak Color in Yellowstone?

I'm thinking about a trip to NW Wyoming this Fall and would like to know if anyone can tell me when peak autumn color is most likely in Yellowstone and the Tetons.

usually the 1st week of October but it can vary by a week either side

I was in the Tetons Sept 23 2010 and the aspens at Oxbow needed at least another week. Last year the NPS was doing controlled burns the first part of October and that caused smokey skies. Wonder if their burn plans have changed to later due to the complaints they likely received.

Howard, First of October for Yellowstone. Week before that for the Tetons.

My experience has been a little different than the others. The colors at Oxbow Bend turn latest in GTNP - around the end of September. The Cottonwoods surrounding the Snake River closer to the entrance of the park change earlier usually by a week to two weeks with the 3rd week of September being peak. Yellowstone isn't known for its color and I didn't see a lot there when I was there in early October (except for backpacking.) You are also running the risk of snow storms at that point in time. My recommendation, depending on how long you have to spend. Work your trip around the dates of September 21 - 31.

The last week in September is usually peak for most of GTNP. I personally didn't mind the controlled burns, I got some awesome photos as a result.