"Police departments deploy most patrol and narcotics police to certain neighborhoods, usually designated "high crime." These are disproportionately low-income, and disproportionately African-American and Latino neighborhoods. It is in these neighborhoods where the police make most patrols, and where they stop and search the most vehicles and individuals, looking for "contraband" of any type in order to make an arrest. The item that young people in any neighborhood are most likely to possess, which can get them arrested, is a small amount of marijuana. In short, the arrests are racially-biased mainly because the police are systematically "fishing" for arrests in only some neighborhoods, and methodically searching only some "fish."5 This produces what has been termed "racism without racists."6"

Source

Harry G. Levine, Jon B. Gettman, Loren Siegel. "Targeting Blacks for Marijuana: Possession Arrests of African Americans in California, 2004-08.” Drug Policy Alliance, LA: June 2010.