Supporters of Amendment 64 smoke marijuana on steps of Colorado State Capitol Building

(CNN) - It didn't take long for the celebrations to begin.

The recreational use of marijuana officially became legal Monday in Colorado, a little more than a month after voters in the state passed an amendment that changed the law.

A group of supporters gathered on the steps of the Colorado State Capitol Building in Denver Monday afternoon, openly smoking what appeared to be pot pipes and joints.

Amendment 64, as it's called, is now a part of the state's constitution, and legalizes the personal use and limited growing of marijuana for those 21 and older. It is still illegal, however, to consume it in public, though there were no reports of any arrests Monday at the Capitol Building.

It also remains illegal to buy or sell marijuana "in any quantity" in Colorado.

Gov. John Hickenlooper opposed the amendment before Election Day, but signed an executive order on Amendment 64.

"Voters were loud and clear on Election Day," Hickenlooper, a Democrat, said in a statement, as he signed the order, making the amendment a part of the state's constitution.

Hickenlooper announced the start of a 24-member task force that would "begin working immediately" to help the state navigate federal laws and establish how citizens can legally purchase and sell cannabis.

Washington, the other state to legalize marijuana in November, officially made the practice legal last week. It could take a year, however, before rules are set for growing and selling pot.

Shortly after Colorado voters passed the amendment on November 6, Hickenlooper cautioned it was too soon to "break out the Cheetos," saying state authorities must work to implement the new measure and prevent individuals from being prosecuted by the federal government, which classifies marijuana as an illegal substance.

In a statement Monday, U.S. Attorney John Walsh said that the Department of Justice is "reviewing" the initiatives passed in both states and that the department's "responsibility to enforce the Controlled Substances Act remains unchanged."

"Regardless of any changes in state law, including the change that will go into effect on December 10 in Colorado, growing, selling or possessing any amount of marijuana remains illegal under federal law," Walsh said.

When Hickenlooper opposed the amendment, he warned that legal marijuana use could "increase the number of children using drugs" and would "detract from efforts to make Colorado the healthiest state in the nation."

"It sends the wrong message to kids that drugs are OK," he added in a statement.

However, with the amendment, Hickenlooper said he would work to enforce the law and make sure that Colorado operates in accordance with the federal government.

"As we move forward now with implementation of Amendment 64, we will try to maintain as much flexibility as possible to accommodate the federal government's position on the amendment," Hickenlooper said.

The task force holds its first public meeting on December 17 and must report its recommendations to the governor's office no later than February 28.

Jim Spellman and Alan Duke contributed to this report.