Legal Question in Construction Law in California

I doubt that you'll find a single law or ordinance mentioning home-made metal forges. Therefore, I'd go on to say that owning a home-made metal forge and keeping it in your back yard is not, per se, illegal. However, California's law books are loaded with statutes, ordinances and decided cases involving zoning, noise, public and private nuisance, and the like. The presence, or more likely the use, of a home-made metal forge in a residential back yard could easily offend one or more such rules -- not because it is a home-made metal forge, but because it is a nuisance or otherwise amounts to a violation of some more general law.