Here are some whitewater rivers to send in California:

Cal Salmon River
Some of the most challenging whitewater in California and flows through California’s Coastal Range in the Trinity Alps
Nearest town: Eureka, CA
River rating: Class IV-V
Season: April – July

North Fork of the American River
Located in between Sacramento and Lake Tahoe and offers some of the most scenic kayaking in the Seirra Nevadas.
Nearest town: *Auburn, CA
*River rating: Class IV
Season: March – Mid-June

Tuolumine River
Yosemite National Park feeds this river and paddlers can expect technical and challenging rapids, intricate boulder gardens, narrow chutes and big drops.
Nearest town: Groveland, CA
River rating: Class III-IV+
Season: March – September

Merced River
Originating high in the Sierra Nevada and works its way through Yosemite National Park. Class IV whitewater in spring then Class III level rapids in the summer.
Nearest town: El Portal, CA
River rating: Class III-IV
Season: April – July

Kaweah River
Starting from the peaks of Sequoia National Park, this river is one of the steepest river drainages in the country. Technical Class IV+ whitewater filled with powerful hydraulics, narrow chutes, river-wide ledges and plenty of boulder-filled obstacles.
Nearest town: Three Rivers, CA
River rating: Class IV+
Season: April – June

Credit: https://www.oars.com/blog/best-whitewater-rafting-in-california/