Contact an Appraiser who provides service in that area and request a retro appraisal on the property for the date needed. It is the same procedure used when determining a date of death value on real estate, when the property owner passess away, for estate tax purposes. Here is a link to search for an appraiser in Glendale, CA 91202 http://www.orea.ca.gov/
When you go the the site, click on the tab "Find an Appraiser" - enter city and zip - click search - you should get a list of active apppraisers in that area that are in good standing. Be sure to ask if they have expierence in reto appraisals - preferably an Appraiser General or Certified General Appraiser.