Males reported that all marijuana-related arrests in California -- including felonies for manufacture and sales -- dropped 70% in the time period studied.

Michael Montgomery, who reports on California's criminal justice system and drug laws for KQED, said he thought the numbers support the argument that low-level marijuana busts had been a significant factor in overall drug arrests. "By taking small-scale possession off the books, you get a significant reduction in the number of people being processed through the criminal justice system," he said.

The ACLU of Northern California put up a post today that also speaks to this point, in terms of the drop in juvenile arrests for a broader array of drug-related crimes:

The astounding 47 percent decrease in overall youth drug arrests revealed by this report also indicates that a large majority of young people being swept into the system are not violent criminals or drug kingpins – they are guilty only of possessing a small quantity of marijuana for personal use.

One of the arguments in favor of decriminalizing possession under an ounce was that doing so would save money. "The question is: how big are the cost savings?" Montgomery said. "We don't know the answer to that yet."

You can see the decline in marijuana and all drug arrests among different categories here.

SB 1449SB 1449

Researcher: Few Adults Arrested For Pot Possession in Calif.; Juvenile Busts Also Plunge