I vote for skipping Yakima, too.

I like spirobulldog's comments.

After more consideration, I realize I might have significantly over-estimated the activities I could potentially do. So back for more advice. Here are a couple of options for day 1 (land in SeaTac at 8:30 am, need to pick-up rental and start driving with overnight plan in Portland.

Option 1 -
Drive from Seattle airport via Enumclaw to Mt Rainier (1:40 min drive), do a 1-1:30 hour short hike, drive via Yakima, Dalles to Hood River to get to Columbia Gorge (4 hour drive according to Google maps) and see some fall colors. Finally, hike to one or two of these waterfalls (Multnomah, Wahkeena, Triple Falls, Wahclela falls).

Option 2- Drive down south along I5 to reach Mt St Helens, followed by Columbia River Gorge (and maybe 1-2 waterfalls from list above)

Even though Option 1 looks more circuitous, Google maps estimates it will take 6:30 hours for option 1 and 5:30 hours for option 2.

Recommendations and feasibility?

Option 1 also has the added benefit of avoiding a higher probability of wet weather; the Cascades create a rain shadow on the east slope, such that Yakima is basically desert. In late October the odds of wet and dismal weather on the west side (I-5 corridor) is quite high, less so on the east side.

You can also use a real-time decision re Mt. Rainier - if it's socked in or wet/snowy (at altitude a possibility) when you're in the area, it's no biggie to just skip it and head straight over White Pass (US 12.) Take comfort that if Mt. Rainier is socked in, you're also saving what would have been a yucky detour to similar/worse conditions at Mt. St. Helens.

If you do skip it and end up getting to Hood River earlier, it's around an hour through the beautiful Hood River Valley (chance of some fall color) up to Timberline Lodge on Mt. Hood, which, IMO, is the equal to, or superior to, Paradise on Mt. Rainier in terms of benefit for a quick visit. Timberline is a little higher than Paradise, but Paradise is snowier on average.

The waterfalls along the Gorge ought to be in fairly good flow if it's been raining for a few days. They're west of Hood River/Cascade Locks, and would probably best be visited the next morning as you head south. If you stay in Hood River, I'd get up early and take the "historic" Columbia Gorge Highway to either Multnomah Falls or to Latourell Falls, which have relatively easy access and adequate parking; then stop for a late breakfast at Shirley's Tippy Canoe (right on the Historic highway just before Troutdale.) Then bang on the freeway toward Portland, or else take the I-205 outer bypass to head south toward I-5.

FWIW here are a couple of pictures from this spring (so use your imagination for autumn.)

Latourell Falls: http://gardyloo.us/latourellefallshdr1.jpg
Mt. Hood from Hood River Valley: http://gardyloo.us/20100509_85a.jpg

I think your last note is on the right path...


and again, I'm STILL of the mind to let the weather (immediately, upon getting your rental car) dictate where you go after Mount Rainier.

I'm still thinking that if it's sunny, you loop Mt. Rainier and go back west to I-5, to St. Helens. Otherwise you go east via "Crack-ima" (as they called it back in the day) (go to Miner's Burgers on South 1st Street for the local tradition, but good luck finishing a burger, fries, and a shake... what I had cost $13 or so {I think} and I had no hope of finishing it).

Right now the weather for Saturday says "AM fog, partly sunny" and sunday is "mostly sunny" - there is HOPE!

(OOPS, CLARITY: )

The weather decision need not happen until you're somewhere circling Mount Rainier... which may let the fog burn off and reveal sunny skies!