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Hello and welcome! My name is ***** ***** I will try my level best to help with your situation or get you to someone who can.
From a purely legal perspective if this is the only person that you have rented a room to in your home, the lodger laws apply and you should be able to have law enforcement remove the person as a trespasser once their notice period has expired.
But realistically, it may be very difficult to get some member of law enforcement to act because they are scared of being sued if they engage in a lodger eviction that later turns out to be improper. So they tend to tell the homeowner that it is a civil matter and they will have to evict the person as any landlord would do.
So rather than trying to fight with local law enforcement to convince them to act, it is typically faster to just go ahead and file an unlawful detainer action in court to get a judgment and writ that the sheriff can execute to physically force the occupant out. This will take about 3 weeks or so once you file the UD action before you can get the sheriff to physically evict the person.
If the person doesn't move out after the expiration of the 30 day notice the landlord can file an Unlawful Detainer (eviction) action. The tenant has 5 days to respond or landlord can file for a default judgment. Once the judgment is final (tenant does not appeal) landlord can get a writ of possession. On the 6th day after getting the writ of possession delivered, landlord can have the sheriff supervise the eviction of any tenant and their belongings.
You are very welcome... The process is pretty simple and you have pretty much already done it.. You give the lodger a written notice to terminate their tenancy that complies with state law (i.e. 30 days) and then once that expires, you can contact law enforcement and ask them to remove the person as a trespasser under CA Civil Code Section 1946.5, Penal Code Section 602.3.
The problem is in getting law enforcement to actually comprehend that they can act and are legally allowed to do so.