Hi David, was this a captive specimen somewhere? Or was it found outdoors in nature? Just curious because this species isn't normally found in California. It's native to the Gulf States. Would be pretty interesting if it's become established in CA, too!
Looks like a female Neoscona crucifera instead. (Nephila clavipes looks different and is only found in the southeastern USA.)
Neoscona crucifera: http://bugguide.net/node/view/864597/bgi...
Nephila clavipes: http://bugguide.net/node/view/155378