Denver - America's first retail stores selling marijuana open for business in Colorado on Wednesday, putting the western state in the vanguard of the country's evolving attitudes on legalising the drug.Officials in the state famous for its ski resorts and breathtaking mountain vistas have issued 348 retail marijuana licenses - including for small shops - that allow for the selling of up to 28 grams of pot to people aged 21 or older starting 1 January. Washington state on the US Pacific coast will follow Colorado several months from now, when it also allows stores to begin selling cannabis.Both states legalised recreational consumption of marijuana in referendums held in November last year, but the new rules coming into force allow cannabis shops.State officials here anticipate that marijuana sales will generate some $67m in annual tax revenue.Colorado's branch of the National Organisation for the Reform of Marijuana Laws (NORML) said everyone will benefit."It will mean jobs, tax revenue for the state and local jurisdictions, increased tourism and a developing progressive new industry in Colorado," NORML attorney Rachel Gillette told AFP."It will also have an impact in that marijuana sales will be brought out of the shadows and the black market," she added.ShortagesMichael Elliott, head of the Medical Marijuana Industry Group, noted that Colorado has licensed medical marijuana businesses since 2010, but said the influx of tourists for recreational use of pot could lead to shortages. "It's tough to know whether supply will meet demand, mainly because it's tough to know the impact of tourism on this new market," he said. "It looks like demand will exceed supply, so I anticipate that prices in Colorado will go up... But as time goes on, more businesses will open meaning there will be more supply," he added.Tax collectors are eyeing the revenue the newly legalised trade will generate, while cannabis growers and others are also rubbing their hands in anticipation.Enterprising companies are even offering marijuana tours to cash in on tourists expected to be attracted to a Netherlands-style pot culture - including in Colorado's famous ski resorts."Just the novelty alone is bringing people from everywhere," said Adam Raleigh of cannabis supplier Telluride Bud."I have people driving in from Texas, Arizona, Utah... to be a part of history."Over the last month I have received somewhere between four to six emails a day and five to 10 phone calls a day asking all about the law and when should people plan their ski trip to go along with cannabis," he added. Medical marijuanaMedical marijuana is already legal and regulated in 19 US states, and has been allowed in some cases for the past 20 years. And in most of them, private consumption of cannabis is not classified as a crime. But Colorado and Washington are creating a recreational market in which local authorities will oversee growing, distribution and marketing - all of it legal - for people to get high just for the fun of it. The market is huge: from $1.4bn in medical marijuana in 2013 it will grow by 64% to $2.34bn in 2014 with recreational pot added in Colorado and Washington, according to Arcview Market Research, which tracks and publishes data on the cannabis industry. Washington state is expected to open more than 300 pot shops in June.State authorities there have received applications for 3 746 marijuana business licenses, including 867 retail licenses, according to The Seattle Times newspaper, which urged caution in an editorial. "Legalisation of marijuana [is] a seismic change in drug-control policy, perhaps the biggest since the end of alcohol prohibition. Supporters and skeptics need to take a deep breath," it said.