For more than 70 years, the sale of marijuana for recreational use has been criminally prohibited in the United States. But that ban, as it has existed for decades, ended Wednesday in Colorado.

The historic first, legal sales of recreational marijuana to those 21-and-older began in the morning at select dispensaries in Colorado -- the first state in the nation, and the first government in the world, to control and regulate a legal recreational marijuana industry.

"This is a big day," said Tom Angell, chairman of drug reform group Marijuana Majority, to The Huffington Post. "With what Colorado is doing now, and what Washington state and Uruguay will do later this year, we're finally getting a chance to show the world the benefits of legalizing and regulating marijuana that we've been talking about for so many years. Bringing the market above ground will generate tax revenue, create jobs and take money out of the hands of the violent drug cartels and gangs that control the trade where marijuana is illegal. Once other states and countries see these proven results, they'll want to get rid of their prohibition laws too."

Voters in both Colorado and Washington approved recreational marijuana in 2012, but Colorado was quick to implement the laws allowing approved marijuana businesses to open on New Year's Day. Washington state's recreational marijuana shops are expected to open later in the year. Uruguay recently became the first country in the world to create a legal, regulated marijuana market for adults.

According to the Marijuana Enforcement Division (MED), the agency that regulates the marijuana industry in the state, more than 300 marijuana businesses in Colorado have begun to receive their state and local licenses to operate legally, but only a few dozen retailers were able to complete the rigorous inspection and approval process in time to open their doors Jan. 1. Those shops will be open Wednesday, selling recreational marijuana for the first time; around twenty are in Denver. Dozens more pot shops are expected to open statewide in the coming weeks and months.

For the shops opening Wednesday, business is expected to boom. Some owners are concerned about supply. “I’m going to run out of cannabis; it’s just a matter of when," said Toni Fox, owner of 3D Cannabis Center in Denver.

To prevent possible shortages, Colorado dispensaries have been preparing for the New Year's rush. Andy Williams, proprietor of Denver's Medicine Man, told HuffPost that he raised his prices months ago, and made larger-than-normal purchases of marijuana alternatives, like edibles. He doesn't think he'll run out, but says some other shops will.

Colorado adult residents can purchase up to an ounce at a time, while tourists can purchase up to one-quarter ounce. However, some shop owners have said they may put a purchasing cap in place at first to preserve supplies.

In November, Colorado voters also approved a 25 percent tax on all recreational-marijuana sales. The taxes are expected to generate roughly $70 million in additional revenue for the state in 2014.

“I think it’s a success story," said state Rep. Dan Pabon (D-Denver), who helped write the state's marijuana law. "But I think it’s actually much broader than a marijuana success story -- this is Democracy and public policy making at its best.”

Pabon also noted that the law is only as good as its enforcement, and that it will truly be tested in the months following Jan. 1.

Not everyone is as supportive as Pabon. Denver Mayor Michael Hancock (D) has been a vocal opponent of marijuana legalization and when asked recently by The Denver Post if he "hated" the idea of marijuana legalization in the state, Hancock replied "yes."

"I have seen the devastation of the progression of marijuana to harsher drugs like crack cocaine," Hancock said. "And a lot of the folks that have dealt with substance abuse -- particularly with cocaine and crack cocaine -- they started with marijuana."

Before voters approved Amendment 64, which legalized marijuana, in 2012, Colorado Gov. John Hickenlooper (D) also voiced opposition to the pot measure, saying, "Colorado is known for many great things –- marijuana should not be one of them." Hickenlooper cited concerns that legal marijuana could lead to an increase in underage use.

However, by the time he signed the law in May 2013, Hickenlooper called it "common sense" and went on to urge federal banking officials to make regulations more flexible for Colorado's marijuana businesses. Marijuana businesses cannot legally obtain normal business banking services due to the federal government's continued ban of the drug.

The Denver Post first reported that neither Hancock nor Hickenlooper would attend the first sales of legal weed on New Year's Day.

Concerns still remain about whether or not recreational marijuana's legalization will increase crime and instances of driving under the influence, and if legitimizing a drug with deep ties to a black market can drive the criminal element completely out.

“We’re cautiously optimistic, you never know what can pop up," said Julie Postlethwait, spokesperson for the MED. "Retail, recreational marijuana is basically a black-market industry, so there’s a lot of things that we will learn in the next couple years -- but if issues arise, we’ll talk about it and figure out how to do it better going forward."

On Tuesday, the Denver mayor's office sounded optimistic about the future of marijuana in the city. "Denver is a vibrant, growing city where people come to make a life, build a career and raise a family," said Ashley Kilroy, executive director of marijuana policy for Hancock. "Medical marijuana has not changed that, and we don’t expect retail marijuana will either.”

For residents and tourists in Denver, the city government recently launched an educational website on the new laws. Some key rules:

It's illegal to give marijuana to minors.

It's illegal to sell marijuana unless you are a licensed business.

It's illegal to drive under the influence of marijuana.

It's illegal to consume marijuana in public.

It's illegal to take marijuana out of the state.

"As a nation, we look back at alcohol prohibition and ask how we could have been so foolish," said Mason Tvert, communications director for Marijuana Policy Project, to HuffPost. "It's time to look forward and put the equally foolish policy of marijuana prohibition behind us."