Tourist Visa (also known as Immigration Permit) is needed for:

Neither a vehicle permit nor a visa is required to visit Rocky Point (Puerto PeƱasco) and other border cities which are classified as "free-zones".

Anyone traveling into the Interior of Mexico regardless of length of stay will need a Tourist Visa.

You can get blank tourist visas in advance of your trip from Mexican consulates in the U.S. and Canada.  You can also get them from the Immigration (Emigracion) Office at border Points of Entry.  Present your proof of citizenship and a completed tourist visa form to the immigration (emigracion) agent for an official stamp before proceeding into Mexico.