In Colorado, famous for its Rocky Mountain ski resorts, officials this week issued 348 retail marijuana licenses including for small shops which from January 1 can sell up to 28 grams of pot to people aged 21 or older.
Washington state authorities 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.
"Legalization 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.
Colorado's branch of the National Organization 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.
Michael 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.
Telluride Bud Co's Raleigh compared decriminalizing pot shops to legalizing same-sex weddings, which are now allowed in more than a third of US states.
"Give it six months, and when other states see that the sky didn't fall and the revenue we are producing, I believe this will spread just like gay marriage," he said. "You just can't stop the will of the people."