The BEST riding in the West -
Would have to be Glacier National Park to Banff and Jasper.
And yes, it has lots of water - i.e. fresh water in the form of lakes.
The San Juan Islands are lovely -
The Olympic Peninsula is great, esp. out to Neah Bay -
The Oregon Coast is stunning -
(although you have long stretches away from the water)
The California Redwoods are awe-inspiring, but inland -
The Mendocino coast is rugged with great views -
And there is no topping Big Sur.
All of that is true.
But you get water and carved mountain peaks in Glacier -
Plus hiker/biker campsites all over the park.
And you can take in Waterton National Park in Canada -
Not to mention riding over to Akamina-Kishinena in BC.
(Canadian parks allow mountain biking on trails.)
From Waterton north there is Kananaskis, Banff, and Jasper.
Eye-popping and a cyclist's dream.
If I had to pick a route in the West -
It would be Jasper, Alberta to Whitefish, Montana.
(North to south so you can do Going to the Sun east to west)
Only about 600 miles - but why hurry?