FLANDREAU, S.D. — The Santee Sioux tribe has proven its business acumen, running a casino, a 120-room hotel and a 240-head buffalo ranch on the plains of South Dakota.

Now the small tribe of 400 is undertaking a new venture — opening the nation’s first marijuana resort on its reservation.

The experiment could offer a money-making model for other tribes seeking economic opportunities beyond casinos.

Santee Sioux leaders plan to grow the pot and sell it in a smoking lounge that includes a nightclub, arcade games, bar and food service and, eventually, slot machines and an outdoor music venue.

“We want it to be an adult playground,” said tribal President Anthony Reider. “There’s nowhere else in American that has something like this.”

The project, according to the tribe, could generate a profit of up to $2 million a month, and work is underway on a growing facility. The first joints are expected to go on sale at a party on New Year’s Eve.

The legalization of marijuana on the Santee Sioux land came in June, months after the Justice Department outlined a new policy that allows Indian tribes to grow and sell marijuana under the same conditions as some states.

A marijuana resort open to the public has never been tried in the U.S., even in states such as Colorado and Washington, where pot is legal.

Not everyone in Flandreau, about 45 miles north of Sioux Falls, near the South Dakota-Minnesota state line, believes in the project. But the profit potential has attracted the interest of many other tribes, similar to the debut of slot machines and table games almost 27 years ago.

“The vast majority of tribes have little to no economic opportunity,” said Blake Trueblood, business development director at the National Center for American Indian Enterprise Development. For those tribes, “this is something that you might look at and say, ‘We’ve got to do something.’ “

Flandreau’s indoor marijuana farm is set against a backdrop of soybean fields. If not for a security booth outside, the building could pass as an industrial warehouse. Inside, men work to grow more than 30 strains, including those with names like “Gorilla Glue,” “Shot Glass” and “Big Blue Cheese.”

Pot is prone to mildew and mold, picky about temperature and pH level and intolerant to tap water. So the Santee Sioux have hired Denver-based consulting firm Monarch America to teach them the basics.

Tribal leaders from across the country and South Dakota legislators will tour the Flandreau facility in mid-October.

“This is not a fly-by-night operation,” said Jonathan Hunt, Monarch’s vice president and chief grower. Tribal leaders “want to show the state how clean, how efficient, how proficient, safe and secure this is as an operation.”

Reider said he hopes marijuana profits can fund more housing, an addiction treatment center and an overhaul of the clinic. Some members want a 24/7 day care center for casino workers.

The marijuana cannot leave the reservation, and every plant in Flandreau’s growing facility will have a bar code. After being harvested and processed, it will be sold in sealed 1-gram packages for $12.50 to $15 — about the same price as the illegal market in Sioux Falls, according to law enforcement.