Legal Question in Real Estate Law in California

Re: Commercial tenants and common area property.

This is the kind of question that almost always has to be resolved by referring to the language of the contract (here, a written lease, I would imagine). Most commercial leases are pretty carefully and comprehensively drawn, at least by larger property managers. Even if the lease doesn't cover the specific situation, there may be some general language limiting the tenant's use of facilities that a court would apply to this situation.

Otherwise, the situation may be governed by the general rules of trespass. Reduced to one sentence, when X trespasses on the lands of Y, Y may (peacefully) eject X and recover damages for harm suffered in consequence of X's trespass.