That is almost always off. The county does not re-assess homes usually for a very long time. So generally the home is worth more than it says. Most people do not ask for a new price because then the taxes may go up! When values went down so much many people did ask for a new assessment as they were paying too much.
This tax record does not matter to you in most cases. The best way to determine value is to have an appraisal done on you home. If this is for court one may want to pay an appraiser for the value, if just for information, call a local realtor. The realtors value will be free and the appraiser will charge about $450 for theirs. The result will be nearly exactly the same!
Prudential CA Realty
Most buyers in today's market know what houses are selling for even if value is less on public web-sites.
If you are talking about county records and you want to lower your public record so your property taxes are less you need to contact your local assessors office and provide them with comps to lower your value and are taxed amount. Usually your Realtor can provide you with some.
Hope this is helpful.