First hire an attorney and demand all documents needed to get this done. Then if he doesn't produce, file a motion to demand the documents. Second, you might need to have a separate hearing in a civil court regarding the boundaries. Please first seek out counsel.
I agree with my colleague. A survey would be the first step.
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Both Greg & Celia are correct. It is imperative that a NEW (corrected) survey be done - and the sooner you have an attorney review the documents the better. In the San Diego area, there are a number of Avvo-listed lawyers who can help with this. See Avvo.com under Find-A-Lawyer, then enter 'Real Estate' and San Diego. You'll see a number who can help you.
I would obtain a title search. This may show what the proper acreage should be. Survey goes off title records, so that's secondary. Court action to quiet title to acreage is ultimate remedy if no cooperation from other owner; but may not be cost-effective based on amount of acreage.