Check out this site. One of the first hits on a general search
http://www.druglibrary.org/schaffer/History/whiteb1.htm
Basically it goes something like this.
The southwest hated the mexicans. The northeast started believing in the whole gateway drug b.s. The mormons controlled utah and couldn't "save" the mexicans.
So they created the marijuana tax act. The AMA said there was no evidence that marijuana did the whole refer madness thing. But as usual, none of the congress members had any clue on what they were voting on, and all it took was one liar to say the AMA supported it.
Then Anslinger said all the jazz musicians were potheads so he could get more agents during a senate hearing. Fastforward a decade later and now its the commies spreading pot. Then it became the mob.
Drug schedules came and the war on drugs followed.