In October, when I was there, the Jenny Lake boat ride had just shut down for the season, as had some of the park lodges. Float trips were also not available.

But I agree that these closures are not a reason to avoid going in October, b/c there is much to compensate for them, mainly the lack of crowds. And for me, the snow was every bit as beautiful as the clear weather. As long as you're prepared, I think October is a great month to go.

You really need to be prepared for anything. We were flying into Denver to do research on Sept 9 - and while the high in NYC was 82 by the time we landed in Denver there was 6" of snow on the ground. It melted the next day - but the high was about 45.

So you need to know what is open and closed - where there are places to stay - and where you can get a car that's properly equipped for the road conditions.

Yes, it seems there's a lot to consider. We will not be going this year. Keeping it (and many other dream trips) in mind for the future.

Thanks to all.

The reason I suggested SLC for your airport is that you can go south to see the southern Utah National Parks if Yellowstone is too cold. The first week of November 2010, DW and I arrived in SLC and drove a rental car to see Arches, Canyonlands, Goblin Valley SP and Capitol Reef. I did have a light jacket for the mornings but shed it for short sleeves in the afternoon.
If you have time you must use in October, look for a place anywhere south of SLC.

Ditto to what tomfuller said. Head to the desert southwest that time of year. Perfect. Zion National Park is another of America's gems.