property line dispute in California

I recently received a notice and a survey map from the attorneys of the new owners of the property behind my back yard that the fence that separates my property from theirs is not on the property line in such a way that there may be about a 40 x 6 ft triangular wedge of land that my fence has enclosed which they claim is theirs. I have owned my home for over the past 5 years without any issue from the previous owners who had lived there for probably over the past 50 years. On first glance, the evidence the new owners, who I am inclined to believe are developers, provided suggests that indeed the fence does not follow the line that the assessors office has on record. I have read about the concepts of adverse possession and prescriptive easements. Their attorney asserts that I would have no claim for prescriptive easements, however, they make no mention of what I may be entitled to by adverse possession. Do I have any claim to that wedge of land or is the law pretty clear that they are entitled to reclaim the land as it appears to be drawn on the assessors maps? They stated that if I do not respond within the next two weeks (12/24/09), that they will proceed to take down the existing wall and presumably the plants and bushes. If the wall comes down, are they required to rebuild a fence, or is there shared responsibility? I would appreciate anyone's thoughts on the matter. The land in question is not particularly useful to me, except for the fact that it may have an effect on the distance between whatever apartment building may be built and my home I suppose. Thanks.What is the name of your state (only U.S. law)?

First, you need to see the actual, in the ground, iron pipe markers that show the claimed boundary lines. See if they look like they have been tampered with. Are there any scratches or grooves down low? That might be an indication that they were pulled up and re-located. Dig around and expose a foot or so of the IPM. What did you see?

If all seems OK, you might be able to get a lawyer to get an extension of the 24 Dec deadline to start the wall demolition.

CA real estate law has been so messed up by lawyers (and appeals) over the last 20 years, The Almighty, Himself, would not be able to take over that wedge shaped piece, in doubt. (Unless the IPM's were moved).