DENVER - Marijuana for recreational use became legal in Colorado on Monday, when the governor took the procedural step of declaring the voter-approved change part of the state constitution.

Colorado became the second state after Washington to allow pot use without a doctor's recommendation. Both states prohibit public use of the drug, and commercial sales in Colorado and Washington won't be permitted until after regulations are written next year.

Gov. John Hickenlooper, a Democrat, opposed the measure but had no veto power over the voter-approved amendment to the state constitution. He tweeted his declaration Monday and sent an executive order to reporters by e-mail after the fact. That prevented a countdown to legalization as seen in Washington, where the law's supporters gathered to smoke in public.

"Voters were loud and clear on Election Day," Hickenlooper said in his statement. The law allowed him until Jan. 5 to declare marijuana legal.

Adults over 21 in Colorado may now possess up to an ounce of marijuana, or six plants. Public use and sale of the drug remain illegal.

Colorado and Washington officials both have asked the U.S. Department of Justice for guidance on the laws that conflict with federal drug law. So far the federal government has offered little guidance beyond stating that marijuana remains illegal and that the Controlled Substances Act will be enforced. Of special concern for state regulators is how to protect state employees who violate federal drug law by complying with state marijuana laws.

Hickenlooper also announced a state task force Monday to help craft the marijuana regulations. The 24-member task force includes law enforcement, agriculture officials, and marijuana advocates.

The governor admonished the task force not to ponder whether marijuana should be legal. "The Task Force shall respect the will of the voters of Colorado and shall not engage in a debate of the merits of marijuana legalization," the executive order read.