It might be. There is currently no law in California prohibiting smoking (including smoking marijuana) in private residences.
You should be aware that California recently passed Senate Bill 332, which expands the availability of smoke-free housing in California by allowing (but not requiring) landlords to prohibit smoking in rental housing units. Effective January 1, 2012, Senate Bill 332 adds Section 1947.5 to the Civil Code. The new law does not force California landlords to prohibit smoking in their buildings, but it gives them the choice to make their properties smoke-free.
Nevertheless, all California landlords owe duties to their tenants, including the implied warranty of habitability and the implied covenant of quiet enjoyment. Under California law, all leases have the implied covenant of "quiet enjoyment". (California Civil Code, § 1927). The landlord (and management company) has the duty to preserve the quiet enjoyment of all tenants. (Davis v. Gomez (1989) 207 Cal.App.3d 1401, 1404.)
Substantial interference is required to establish a breach of quiet enjoyment. An interference by the landlord "by which the tenant is deprived of the beneficial enjoyment of the premises amounts to a constructive eviction if the tenant so elects and surrenders possession, and the tenant will not be liable for rentals for the portion of the term following his eviction." (Kulawitz v. Pacific Paper Co. (1944) 25 Cal.2d 664, 670.)
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult your own attorney.
Although I am not 100% sure, I believe that a landlord has the right to restrict all smoking (of anything) on any deck or outside area. I also believe that there are laws currently under consideration to restrict smoking that could cause second hand smoke.
If the smoke bothers you, it could be considered a private nuisance, but that would be hard to prove. I would talk to your neighbors about it first and see if you can resolve this informally.
Since Marijuana smoking is illegal, except if they are using it for medical purposes, you might inquire about that.
This is general legal advice intended for informational purposes only and does not create and attorney/client relationship. If you wish further advice, please contact an attorney of your own choosing or you may contact me for further advice and make other arrangements including retaining my services.