The amount of Colorado marijuana being seized en route to other states through the U.S. mail has more than quadrupled since 2010 and was destined for more states than before, according to a new report by a federally funded drug task force.

Postal inspectors seized more than 493 pounds of pot from packages in 2013, up from 57 pounds in 2010, the year after medical marijuana dispensaries proliferated in Colorado, according to the figures released this month by the Rocky Mountain High Intensity Drug Trafficking Area.

Just 15 packages were bound for 10 states in 2010, compared to the 207 parcels destined for 33 states in 2013. Top destinations were Florida, Maryland and Illinois, the report states.

Colorado legalized marijuana for all adults over 21 in 2012. The report, based on information from the United States Postal Inspection Service, doesn't contain figures for the first six months of 2014, when recreational pot shops opened in the state. The Postal Service in Denver has denied requests from The Associated Press for the same data.

The spike in pot seizures is a sign not of more proactive postal investigations but that more people are shipping pot through the mail, said Tom Gorman, director of Rocky HIDTA, a network of law enforcement organizations in four western states that share information on drug-running patterns. It releases a yearly report about marijuana legalization as part of its work.

Despite being legal in Colorado, federal law maintains marijuana use and sales are illegal. Because the Postal Service is a federal agency, using it to move marijuana — even within states where it is legal — is a crime.

Denver attorney Brian Vicente, who helped write the pot law, said the leakage of Colorado marijuana into other states is a serious issue that voters agreed should remain illegal. But he was skeptical of the HIDTA report, which he said promotes prohibition.

The U.S. Justice Department said it would tolerate marijuana sales in Colorado and Washington as long as the pot didn't cross state lines. But federal authorities rarely pursue cases involving small-scale marijuana smuggling.

A spokesman for the U.S. Attorney's Office in Denver said some cases remain under investigation.

"We're supposed to eliminate the black market, but we've become the black market for so many states," Gorman said. "It's all about making money for most of these people. I send you marijuana or edibles, and you pay me for it, and I can get a lot more money by trafficking it to states where it is illegal."

He said people are also sending it through private couriers like FedEx and UPS, which don't release statistics on their seizures. Neither company would comment on how it investigates such cases.

Postal inspectors haven't changed their enforcement approach despite the "uptick in marijuana leaving the state," said Denver-based U.S. Postal Inspector Pamela Durkee, who would not elaborate. She said the focus remains on thwarting and dismantling large-scale enterprises and organized groups that send high volumes of pot and narcotics.

"We wish we had a few extra bodies, but we don't see the challenges as being a lot different than they have been in the past," Durkee said.

Gorman said much of the illegal exports come from people who grow their own plants either at home or in warehouses. State law allows adults to grow up to six plants, though doctors can recommend more for medical patients. The complexities of the law make it difficult for police to enforce high-volume grows.

Among the cases listed in the report:

— A Lakewood, Colorado, man who police say used his condo and a warehouse to grow enough high-grade marijuana for his crime ring to send between 24 and 60 pounds each month to out-of-state customers.

— A Boulder, Colorado, man who sent more than 14 pounds of pot to places including Wisconsin, Massachusetts and California.

— A suburban Denver drug task force seized nearly 20 pounds of pot from three FedEx packages bound for Illinois and Kansas.