The assessor value is based on when the current owners bought this home and has no bearing on current market value. Your best way to find the true value is to ask your REALTOR(R) to do a CMA (Comparative Market Analysis) on this home. The CMA will tell you what homes have sold for in this neighborhood in the last few months, and with your REALTORS(R) guidance, you will not overpay. Since this is a short sale, be aware that the asking price may or may not be approved by the lender. Your REALTOR(R) can explain short sales to you in depth. Best of luck in your home search.
agent - Leanne Smith
I'm not sure about the market in California, but here in Minnesota tax assessed values are finally catching up (and passing) actual market values.
Each County has a different set of standards for how often they assess a home. Check with Riverside County - http://www.countyofriverside.us - to see what their requirements are. Typically this information can be found under the property records section.