"Today Mexico is a major producer and supplier to the U.S. market of heroin, methamphetamine, and marijuana and the major transit country for cocaine sold in the United States. According to the Department of State’s 2009 International Narcotics Control Strategy Report, as much as 90% of the cocaine entering the United States now transits through Mexico. A small number of Mexican DTOs control the most significant drug distribution operations along the Southwest border. The criminal activities of these Mexican DTOs reach well beyond the towns and cities of the border, extending along drug trafficking routes into cities across the United States. The Mexican DTOs have exhibited many characteristics of organized crime such as being organized in distinct cells and controlling subordinate cells that operate throughout the United States.1"

Source

Beittel, June S., "Mexico's Drug-Related Violence," Congressional Research Service (Washington, DC: Library of Congress, May 27, 2009), p. 7.
http://www.fas.org/sgp/crs/ro…
citing: United States Department of State, Bureau for International Narcotics and Law Enforcement Affairs, "International Narcotics Control Strategy Report: Volume I, Drug and Chemical Control," (Washington, DC: U.S. Department of State: March 2009), p. 414.
http://www.state.gov/document…
and Cook, Colleen W., "Mexico's Drug Cartels," Congressional Research Service (Washington, DC: Library of Congress, October 16, 2007), p. 5.
http://www.fas.org/sgp/crs/ro…