Locally, Delores Conway, director of USC's Casden Real Estate Economics Forecast, points to Riverside County as ground zero -- a place that was overbuilt, with new homes now being discounted by builders, and that is witnessing a sea of foreclosed homes on the market, with more expected. RealtyTrac reported last week that Riverside County led the state in foreclosure activity with one in every 330 households affected. Neighborhoods that just a year ago were flourishing are today blighted with house after house of "for sale" signs and properties abandoned to foreclosure. How did this come to be? The crisis in the sub-prime mortgage industry doesn't shoulder all the blame, experts say.