I am really enjoying this thread as we will arrive for our first Yellowstone visit 4 days after you. The book
Yellowstone Treasures by Janet Chapple (free shipping right now on it at amazon) was recommended to me so I thought I'd pass along.

Mary Fran,

If you are interested in geology, Yellowstone is the place for you! With 3 nights at Snow Lodge, you should have time to take one of the ranger hikes/talks, if they are given that early in the season, on the Yellowstone area.

Also, there was an excellent, facinating NOVA special on the Yellowstone caldera a few years ago. It was absolutely awesome and really made you think......maybe you can get it at a library or on line? Highly recommend.

Just hope it doesn't blow in our lifetime!

Well, one question answered: Late May is too early to reliably plan a trip to Yellowstone. We cut short our trip before we reached Yellowstone, and we returned home early, because it was too cold, rainy, and snowy, especially above 5,000 ft. altitude in Montana.

On May 21st, we were en route to Anaconda from Missoula on a leisurely trek toward Yeallowstone from Spokane, and we made a side trip to Phillipsburg, where my grandmother had lived in the '40s.

Phillipsburg is just a charming old-west town, and we were enchanted with the restored buildings on the main street. However, it was so cold, and then it began hailing, so we pressed on toward Anaconda. That night, 16" of snow fell in Phillipsburg.

Very cold weather, with mixed snow and rain and fog, followed us to Deer Butte, where we looked at each other after a good night's sleep, and said, "Let's go home to Spokane, where the sun is shining."

The trip definitely was not a waste, as we saw great country between Spokane, Bonners Ferry, Idaho, and Kalispell, Flathead Lake, Missoula, and Philipsburg.