The route that #6 has given you is something snatched off of MapQuest and not backed up by personal experience. And his advice about accommodations at Bryce and Zion is simply wrong. Once the tourist season settles down after Labor Day (first Monday in September), it's not particularly hard to get a room at park lodges. Hell, I snagged rooms at Zion and the Grand Canyon at the very top of the tourist season, late July and early August, in 2005. Took a bunch of calling and time on hold, but I did it. Late September would be a piece of cake.
That said, I wouldn't advise #6's more easterly route. In practical terms, it would chew up more time than he thinks. I've driven those roads and been to those places (except for Bryce), so I know.


Disregard the advice to go to Bryce and Zion. These are fantastic places -- Zion I've seen, and I know Bryce by its reputation -- but they are considerably out of the way. If you had more than five days, I'd have advised going there and given you the route, which would have included the Grand Canyon as well. But you just don't have the time. Beware the TT pitfall of travel advice from people who haven't actually driven the routes they suggest.

One more thing: Click on my egotistical profile to get a sense of my qualifications to give you the advice I've given.

One one more thing (sorry, but TT's software doesn't allow for editing of posts). If you take the route I've given, you'll really get a sense of how the countryside changes between the Pacific Northwest and Las Vegas. You'll go through mountains, forests, high desert, alpine lakes and low desert. If you take Interstates to Bryce and/or Zion parks, you'll be racing around and seeing very little solely for the sake of catching a couple of trophy destinations. That's not travel, that's theme parks.
Noted American author John Steinbeck wrote that the Interstate highway system made it possible to drive 3,000 miles and see nothing. He was exactly on target.

the routes suggested sound like ample driving and seeing so i'm pretty happy - guess i'll have to discuss with my other half whether to do more scenic driving throughout or quick buzzes with concentrated viewing in national parks. by the way, would there be camping facilities along this route at all? thanks so much for a the discussion - it's really useful!

Hey, Willysnout, dont get nasty. I have in fact been on that route. Time was taken from Mapquest. The lodges can fill up early. If you disagree with advice given to help someone, just offer better advice. Dont act like a disgruntled child.

OP, I don't camp out so I can't answer your camping question other than to say that I'd be surprised if you couldn't find places along the route I've suggested. It's your trip, and you ought to do exactly what you want to do. I would note that I routed you through two national parks and along two (three, if you include Lake Tahoe) natural features that are, by all accounts besides anything I might say, fantastic places to see. The problem with an Interstate-heavy route through the West in search of two particular national parks is that you're just not going to see a whole lot in between.
But if you do decide to go to Bryce and Zion, then you really should find a way to also see the Grand Canyon. It is on the way, more or less, from Bryce and Zion back to Vegas. See FAQ post 131: "The Grand Canyon" for more information. Oddly enough, you won't even make better time on the Interstates between these points, because the two-lane roads I've given you are remote and have very light traffic.
BubbaK, you're right about me being harsh, but I do have a point. MapQuest is a useful tool. I used it in my advice, too. But I think it's a real disservice just to hop onto Mapquest, calculate distances via Interstates and tell someone to take a route. As for the lodges,they fill up early if you're talking about high season, i.e., mid-June through early September. But the OP is taking this trip in late September. Finding rooms in those lodges will not be a problem.

If you decide to take the route Willy suggests, be aware that you won't be able to do the first part of it (in Washington). Hwy 123 is washed out and will not be repaired this year. As an alternative I'd suggest following his directions to 410, and take the detour to the Sunrise Visitor's Center area of Mt. Rainier off of 410. Rainier is so gorgeous and you won't see any other big icy volcanoes, close up, on your trip. Then go back to 410, go over Chinook Pass (very pretty drive), and stay on 410 until it meets hwy 12, which you can take to Yakima and continue on with the trip Willy suggests.
I would find the time to visit Zion National Park, though it isn't exactly on the way (but it's an easy 2.5 hours from Vegas). I would go there over Death Valley anyway, though DV is more on your way.
I've been told by tour and hotel operators that May and September are the busiest months in southern Utah. SO many people (like me) go down to hike, mt. bike, climb, etc, and want to avoid the heat of summer. I wouldn't chance reservations.

Oh, and yes, there are tons of places to camp, but I think we need some fairly concrete locations before giving suggestions. You will find campgrounds mostly in National Parks, State Parks, and National Forests, so you could, for instance, google Oregon State Parks to see what your options are if you are staying the night in Oregon.
And I forgot to say-there's some really neat scenery and geologic features in the Bend, Oregon area, like Newberry Crater National Volcanic Area and Smith Rock State Park. There are many campgrounds in the area if you stay the night.