The marijuana market is twice the size in US Dollars vs. the cocaine market and nearly half the volume of the overall drug trafficking.
http://www.talkingdrugs.org/report-global-illegal-drug-trade...
http://www.talkingdrugs.org/report-global-illegal-drug-trade...
Edit: Some googling produces estimates ranging from 30 to 70 percent imports, depending on the point the article is trying to make, so let's just call it 50% domestic nationwide.