Sierra south will have local beta. The newest guidebook I know of is called the best whtewater of Califorina, by Stanley and Hollbeck. THere is good boating for all abilities and styles in the vicinity, water levels permitting.
If you're going to be in the area surrounding Kernville, by all means check out Dry Meadow Creek as well as Brush Creek and Peppermint Creek. DMC is class five pool-drop, and has been featured in various paddling videos and magazines. It's probably the most well documented run within the state of California or the entire west coast for that matter.
The Kern River offers offers flatwater to class V with lots of raodside access along with several wilderness trips within it's watershed. IF you're looking for something to truly test your mettle, the headwaters of the Kern requires a 23-mile hike to the put-in through Sequoia National Park. The benefits, I guess, is that you'll get to see the backside of Mount Whitney, and somewhere along the river you'll pass through a valley with granite walls on par with those found in Yosemite. Read advanced class IV-V paddling skills required if you do choose this section of the Kern.
If it is raining hard when you're there, another option are the creeks of Southern California: Sespe, Malibu, and Dinkey Creeks. A great website is Somewhere Out There: Out and About in Southern California. Type it into a search engine and is shoud bring it up. THe Kings and Kaweah Rivers offer plenty of boating as well. Hope this helps.
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