My question involves landlord-tenant law in the State of: California (San Deigo)

I'm a landlord. My tenant has stopped paying his rent. I've received nothing for 6 months.

Rent is due 1st of each month - last payment was Nov 2011.
30 days notice required by both tenant and landlord to terminate lease
Pets permitted ONLY with signed pet addendum and additional pet (security) deposit
NO subletting
Landlord (me) pays for water and electricity
Guests who spend more than 2 nights at the house need to be approved in writing (with addendum) by landlord

I notified my tenant (24 hrs in advance) that I would be stopping by the property. I was hoping to discuss his lack of payment. Instead, when I arrived, a complete stranger answered the door...along with a barking dog. This person assumed I was a friend of my tenant and informed me the tenant ususally comes to the house on a Wednesday. It sounded like my tenant is living with his girlfriend and no longer stays at the house he has rented from me...but I can't prove that. I left without entering the home.

My tenant later contacted me...explained he had been out of town for a few days and the person at the house was simply house-sitting for him for a few days. It was clearly a lie. I can't prove otherwise, however I'm confident this person is actually living at the house...complete with his unapproved dog. Whether he is paying my tenant to live there or not is another story...and something I wouldn't be able to prove anyways. I will be issuing my tenant a 30 day notice to vacate....and of course, will pursue having him evicted if necessary...minimum of 90 days, if not longer.

My question is in regards to this person currently living there. I have since confirmed he is still at the house...with his dog. Do I have the right to ask him to leave? Can I have him evicted? He is not on the lease (I don't even know his name) and has no right to be living there. My tenant does not have the right (per our rental agreement) to sublet or allow him to live there. This person also has a dog inside the house without my permission and with no deposit or addendum as required by the lease. Seems to me he's not a squatter and is basically a trespasser with no rights. If the lease does not permit him to live there, and does not permit the dog to be there, can I do anything? Can I force him to leave? Or will I have to allow a stranger to live in my house for 90 days or more while I pursue eviction over my tenant and not the person living there illegally...????

Thanks in advance for any help or advice you can give...this is a new situation for me....