Legal Question in Real Estate Law in California

Homeowners' insurance pretty much always excludes any form of earth movement. As for who has to maintain the wall, that depends on how the land was graded to create the two lots. I'm assuming there was a slope that needed to be turned into level pads fro the two houses. Creating level pads on a slope can be done one of two ways, or by combining them. You can "cut" or "fill" or both. You can't build the house on fill, but pads, patios, fences, etc. can be. So the question is whether the wall is holding back fill that was added to your lot, or a cut that was made to level his lot, or both. The neighbor would be responsible for the wall if it holds back a cut where soil was removed to level his lot. You are responsible for it if it holds back fill that was added to level your lot. You are jointly responsible if it was created by a combination of cut and fill.