The "adult use" cannabis will be sold with a 25 percent tax—three times as much as Colorado's medical marijuana tax. Will recreational users pay more for legal pot? That is the $240-an-ounce question.
Weedmaps, the Yelp of medical pot, is getting a jump on events. It's rating and reviewing medical dispensaries in Colorado that also will sell recreational pot.
(Read more: High Times aiming for $100M marijuana fund)
Listings include "3D," a dispensary that on New Year's Day will become the first retail outlet for adult-use pot. Supporters are planning a news conference as the store opens its doors.
"The first customer on January will be Sean Azzariti, a Denver-based Iraq war veteran who can now legally use marijuana to alleviate the symptoms of post-traumatic stress disorder," said a press release announcing the event.
How smooth the transition from illegal to legal, from medical to recreational, will be is up for debate. Washington's first retail outlets are not expected to open for another few months, as that state has been overwhelmed by license applications.
(Watch: Colorado rolls with retail marijuana)
Colorado has run into obstacles with regulating medical marijuana, which may not bode well for the recreational market, according to The Wall Street Journal.
"Dozens of medical-marijuana growers and dispensaries are still operating without full licenses as Colorado officials work through a backlog of requests originally filed in 2010," the newspaper reported this week. "A state system that uses software and radio-frequency ID tags to monitor pot production and sales launched only recently, drawing complaints from businesses, which say it is cumbersome and costly."
Both Colorado and Washington have become magnets for patients seeking different forms of cannabis, such as pot in an edible form, that can be used to treat medical problems.
One of the latest is a toddler from New Jersey who suffers from severe epilepsy. Vivian Wilson's family is moving across the country to Colorado, frustrated by the Garden State's pot laws, which limit sales to smokable marijuana.
(Read more: Seattle throws birthday party for legal pot)
This coming year will witness dramatic growing pains of an industry coming out from the shadows, a rollout that many hope will create a tax windfall but that others fear will have unforeseen negative consequences.
Change begins Wednesday in Colorado, and the Justice Department will be watching. No state has done more to start a regulatory process from the ground up in an effort to make the system work and keep federal authorities at bay. An official with the state's Revenue Bureau told the Journal that Colorado is "blazing a new trail"—an interesting choice of words.
Rocky Mountain High is about to get down to business.
—By CNBC's Jane Wells; Follow her on Twitter: @janewells