Re: How to Force a Neighbor to Remove a Wall or Pay Assessments
Couple of things to consider. In CA, unless it can be shown otherwise, a fence or other enclosure such as a wall built for the purpose of separating the properties from each other is presumed to be owned jointly by both owners unless it can be shown otherwise. Next, even if your neighbor supplied all the labor and materials, if he built what was intended to be a boundary fence with your permission and understanding that it was intended to be a boundary fence, then you share responsibility for having to remove it. Your permission didn't necessarily need to be express permission either. If you were aware of his building it and its purpose and you made no attempt to prevent him from doing so, then it may be presumed that you planned to enjoy the benefit of having an enclosure on that side of your property and we're back to the shared responsibility.
If your neighbor just built it of his own accord without consulting you and you had no reasonable opportunity to prevent it's construction, then it doesn't matter whether he built it on the line, on his side, or on your side. It's his property and his responsibility. Going to the City Building Department and explaining this situation to the Director or other senior building official should clear the citation for you.
I'm a surveyor, not your surveyor & not an attorney.
Advice is general survey, not legal. Hire a local professional for specific advice.