... so we are thinking of heading back down to LA through San Francisco. We haven't got weeks and weeks, only a week! What would you recommend? I was thinking of doing Montana-Salt Lake City- SFO but is going through Seattle shorter? The wedding is somewhere near Flathead Lake...
instead of worrying about time / getting lost in te desert...
With the web of Interstate, Federal and State highways along your route, getting Lost in the desert would take an effort! The area around Flathead lake is really nice. You will be so close to Glacier National Park...Maybe you should kick back a while there?

Your stated return route would be fine -- plenty of cool things to stop and see, but since you asked... I would drop down to I-90 and stop for a coffee or two at Coeur d'Alene, Idaho (gorgeous lake) and then cut through Spokane and pick up US-395 and drive through the Columbia Gorge (either on I-84 on the southern side -- or my choice -- Oregon Route 14) or a combination of the two to Portland. If you like great bread... my cousins own The Grand Central Baking Companyin Portland... but I digress...

From Portland, I would zoom over the coast and follow US-101 down to Reedsport (awesome kite flying in this area) and then tack back eastward to I-5 and go south to Grants Pass. If you have time -- take the day and go to Crater Lake National Park. -- Lots of amazing mountain vistas here.

If time is short, consider taking US-199 from Grants Pass to US-101 at Cresent City, California. -- Take a walk in Redwood National Park -- and then if you have time and like coastal drives you can meander down California Route 1 (here is a great guidebook ) or you can use the faster route US-101 to San Francisco.

Spend a day in and around the Bay area and then either go back to the coast via California 1 or you could zig-zag your way south to LA. Lots of posts on this board about routes between San Francisco and LA.

Mark