If you can drive to Walnut Creek, which is fairly close, you can use the appraiser Nancy Stacy - she is listed in the appraiser section on Pricescope.
If not, then look in the yellow pages for independent appraisers without jewelry store affiliations. Quiz them on the phone to see how long they have been in business (go for more than 5 years) and what certification they have. I would choose a graduate gemmologist (GIA). Good luck.