The Federal Reserve does more than just slash interest rates below the rate of inflation. In the case of the New York branch of the Fed, they also provide the nation’s nerds with really cool interactive maps showcasing various tidbits of mortgage data. The server is pretty bogged down right now but you should consider visiting the afore-linked page sometime soon, as it offers loads data on the state of both subprime and Alt-A mortgages (the latter basically being high-risk loans made to borrowers with good credit). The site stopped working before I could verify this, but it looks like you can drill down for data specific to San Diego County and even to each ZIP code within the county. (Thanks to the blog Calculated Risk for the link).
— RICH TOSCANO