Jacob Sullum preaches:
The authors of the [Drug Policy Alliance] report, led by Queens College sociologist Harry Levine, found that from 2006 to 2008 "major cities in California arrested and prosecuted Latinos for marijuana possession at double to nearly triple the rate of whites," despite the fact that "U.S. government surveys consistently find that young Latinos use marijuana at lower rates than young whites." [...]
[T]he drug war's de facto discrimination against blacks and Latinos adds insult to injury. Leaving aside the explicitly racist roots of drug prohibition, when you have a law that 1) criminalizes widespread consensual activity and 2) is enforced against only a small subset of violators, there's a good chance it will impose an extra burden on vulnerable minorities. The fact that affluent, politically influential white people get away with the same drug offenses that land poor blacks and Latinos in jail makes this legal regime even more arbitrary and unfair. Furthermore, as the Prop. 19 debate shows, this aspect of the drug war's injustice can attract allies in the fight to overturn prohibition who otherwise might not focus on the issue.
(NORML has more charts and statistics.)