I'm particularly interested in the Southwestern parks (Grand Canyon, Bryce, Zion) and the Northwestern parks (Glacier, Yellowstone, Olympic). I assume July and August are popular and must be booked far ahead. When do reservations for 2007 open? When do July-August slots fill up? When do weather conditions in the NW ones preclude visiting? (we're seniors)

Most of them accept reservations 365 days in advance. In 2002, I was able to make reservations at Zion, Yellowstone, and Glacier. I made them in early Feb. for early June. Bryce was already booked and Yellowstone were the last two cabins available for the dates.

You may be too late to book rooms in the nicest lodges in those parks.

September and early October would be good months to visit as well. You *should* be able to see Yellowstone and Glacier yet without worrying about snow, although that is a possibility. Certainly the crowds would be much smaller.

Are you doing all of these on one trip? If so, and you're willing to go other than in July/August, I'd start with Glacier/Yellowstone/Olympic shortly after Labor day, and then head to the others after that. Lodging may be an issue already, but it should be possible to get a spot somewhere if you keep checking.

One thing to keep in mind is that some of the accommodations and restaurants close after Labor Day. In-laws did Yellowstone last year in September and most of the lodgings were closed by mid-September.

Just looked at Xanterra's website (they run the in-park lodges at Grand Canyon, Bryce, Zion and Yellowstone). They are taking now reservations through September '07 for GC, Bryce and Zion, and through February '08 for Yellowstone. Book your dates as soon as you know them, and keep trying if you don't get the dates/places you want because cancellations will occur.

Your best bet is to go to http://www.nps.gov/ and check each parks web site you plan to visit. You will find a wealth of information there. Each has a page with the opening and closings of roads, services and lodgings as they pertain to that park.... Just remember when school is out the parks have more visitors. Prim time is July and August. Good times for Yellowstone and Glacier are mid June and after Labor Day in early September.