If you're looking to buy homes at auction on the courthouse steps, then services like RealtyTrac can be helpful. However, be aware that the "prices" are the amounts due on the mortgages being foreclosed, and are not necessarily the "sale price". You'll find homes on RealtyTrac that are valued at over $1 million "listed" at $40,000, simply because that's only one of the mortgages on that home.
The homes on RealtyTrac are NOT being offered for sale, they are homes in various stages of the foreclosure process. Many of these homes will have multiple mortgages, so if the mortgage showing up on RealtyTrac is not the first mortgage, be aware that the first mortgage holder must be satisfied before these lesser lien holders can get paid.
The majority of these homes will not end up being auctioned on the courthouse steps. They will either be sold as a short sale (pre-foreclosure) via a listing on the MLS, or the "sellers" (current owners) will work out a payment plan with their bank and remain in the home. The foreclosure process in California is a lengthy one, lasting a minimum of 120 days before an auction date can be set. Often the auction date is extended while the current owners list their homes for sale as short sales and accept offers from potential buyers.
If you're looking to buy short sales (pre-foreclosures) and bank-owned homes, check with a local Realtor. They'll be able to provide you with the latest information on short sale and bank-owned homes for sale, and help you through the lengthy short-sale process.