Before everyone starts foaming at the mouth about California, I believe the OP is neither a permanent resident, nor a US Citizen. As such, this is a Federal restriction, rather than a State one.
18 U.S.C. 922(g)(5)(B) and 922(y)(2); 27 CFR 478.11 and 478.32
An alien admitted to the United States under a nonimmigrant visa is prohibited from shipping, transporting, receiving, or possessing a firearm or ammunition unless the alien falls within one of the exceptions provided in 18 U.S.C. 922(y)(2), such as: a valid hunting license or permit, admitted for lawful hunting or sporting purposes, certain official representatives of a foreign government, or a foreign law enforcement officer of a friendly foreign government entering the United States on official law enforcement business.”
So, you can rent one, but not own one.
Even legally here on a visa, he still needs to establish a residential address, which is where the 90 days comes in.