Legalization or outlawing of anything in America follows a downward flowchart system that begins with the federal law and ends with city ordinances.
There are two forms of law at the federal and state levels: common law and statutory law.
Common law is court made through published higher court opinions; it is based on courts interpreting both constitutions and the constitutionality of laws, as well as the applicability of laws.
Statutory law is legislature made; it is based on legislatures enacting fully binding laws on the relevant citizens.
Thereon, the key understanding is that a lower level system of laws cannot contradict or go against a higher system of laws.
Ultimately, legalization of marijuana - if not outrightly banned at the federal level by federal statute - can then be legalized at the state level through repealing or amending a state's laws prohibiting recreational marijuana posssession and use. This decision rests in the hands of a state's legislature (typically called General Assembly).
If it is legalized at the state level, then more specific considerations can be made within city municipality levels as well. However, this is unlikely - city governments will likely simply mirror state law on such a matter.
More than likely, marijuana is an issue that will continue to be handled at the state level as long as the federal government does not go out of their way to ban marijuana sale, possession, and/or use - we see an extension of this concept with CBD oil recently.
