Your friend most probably does not have any rights, and will have to leave.
In California, the elements necessary to establish ownership of real property by adverse possession are as follows: “(1) the payment of taxes, (2) actual possession which is (3) open and notorious, (4) continuous and uninterrupted for five years, (5) hostile and adverse to the true owner's title, and (6) under either color of title or claim of right.” (California Maryland Funding, Inc. v. Lowe (1995) 37 Cal.App.4th 1798, 1803.)
Therefore, unless your friend had been paying the property taxes, becoming the owner through adverse possession is not likely.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult with your own attorney.
Probably none. You mention something about the railway, I believe it is not possible to adversely possess railroad land. Secondly, even if it were possible, I doubt all the elements of adverse possession have been met.
Assuming there was legitimate adverse possession, were the structures built without permits? If so, then the city could have them condemned.
If the police are involved, it is possible that failure to comply will result in arrests.
I agree with my colleagues that it is unlikely that adverse possession is a tool that will work here. If the police are now involved, it is likely that if your friend does not voluntarily move, he may return someday to find all of his belongings carted away. Best he take control of his destiny and move first.
I have been licensed to practice in the State of Oregon since 1990. I am not offering legal advice regarding your question, only general information regarding the law. You are not my client nor am I your attorney unless we sign a retainer agreement.