These are all good ideas, especially Bugs saying be flexible due to forest fire smoke.
The Southern 1/3 of the Oregon Coast is moderately entertaining. The northern 2/3s is a tourist trap suitable for leisurely pursuits, seeing museums, watching sunsets hiking, flying a kite and the like. The Oregon Dunes are near Reedsport and you can rent a dune buggy and go play. The most
impressive view along the Oregon Coast is at Cape Sebastian.
The California coast is foggy a lot in the summer and this includes September. It will be 55 degrees along the coast and 85 or 90 five miles inland. If this is the case head for the mountains.
I will take a different approach here in recommending roads.
Oregon
One thing about Oregon. Gravel lines the road's shoulder so there is gravel in right hand turns. It is nasty.
Hwy 245. This maybe a bit out of the way but it is one fine road.
Hwy 218. The best road in Oregon. Period. The Rueben run is near enough to do this in a day.
Hwy 38. The second best road in Oregon. Tyler included this road in the route above.
Along the coast from Brookings Oregon to Legget Ca two hundred miles and a bit of a yawner. The Redwoods are the attraction here.
California
For masochistic try the
goat trail, called the Mattole Rd, out to the the Lost Coast. It is paved - at least most of it. The bonus is you can see great
views of the ocean in a pastoral setting with cows on the beach. I will never ride an FJR on this road again. I might do it on a Dual Sport bike with lots of suspension travel weight less then 400 lbs.
Hwy 1 from Leggett to Westport. This is one of the better roads in California. Simply awesome. Interestingly enough this is the twistiest bit of Hwy 1 and it is not along the coast.
Hwy 1 from Westport to Fort Bragg. Pretty entertaining pavement right on the coast.
Fort Bragg has good accommodations for a good prices. In fact this is great place to spend a day or two and do some
loop rides.
Hwy 36. One of California's finest roads. Just outside of Red Bluff you will find this:
Hwy 1 from Monterey to Morrow Bay. Great road if it is not foggy. If you choose this road you will likely go over the Golden Gate Bridge down along San Jose. It is a bit of slog and timing is everything. If you chose the Golden Gate don't miss the
View Point. Hwy 1 from San Fransisco to Santa Cruz is a bit boring.
California Mountains!
Hwy 70. Follows the Feather River. Some nice cruising but tight turns are lacking.
Quincy to Orville. One of the top 10 road in Northern California. Not to be missed if you choose the mountains.
The La Porte Road. For a grand day ride this and the Quincy to Orville Road.
Hwy 49. Very nice and even has a morbid deadman's turn sign courtesy of a home owner.
The there is the Passes in the Sierras. Wow! Great fun. Find Hwy 50, Hwy 88, Hwy 89, Hwy 4, Hwy 108 a personal favorite, and Hwy 120
.
Hwy 245. A great road south of YFO. Want to avoid the Yosemite crowds go here. Might be a stretch for a day ride and there is no good way to get there aka you get dumped into Fresno. Avoid the Yosemite crowds by leaving at first light.