From the Grand Canyon, if you don't mind a bit of driving, go west to Boulder City, then up 95 to Beatty and Rhyolite (motels at Beatty; Death Valley to the west), Goldfield and Tonopah (motels at Tonopah), then cut west through Montgomery Pass to Yosemite Park. This is western country that you will never forget although long since bypassed as worthless). Carry a couple of sixpacks of water.
From Yosemite, an interesting drive to Stockton (an inland seaport, connected to San Francisco Bay by a channel), then several routes into the San Francisco Bay area.

I have done the Pacific Coast Highway from The Olympic Park area, following 101 and 1 for the most part, all the way to San Diego, mostly in parts, but it should be a separately planned trip. Much to see, many side roads to explore, and really too much for a single trip.
Zion is a son's favorite area for a biking break, but I haven't been there, although I have covered much of the Navajo reservation and NW New Mexico area.