Authorities are investigating a marijuana growing operation in a large swampy wildlife management area in Cass County.

About 5,000 marijuana plants were discovered in the Meadow Brook Wildlife Management Area in September, according to a search warrant affidavit filed Dec. 27 in Ramsey County District Court. Authorities filed the affidavit in order to obtain patient information connected to a prescription pill bottle found at a grow site.

According to the affidavit: In the fall of 2011, the Cass County Sheriff's Office asked the Minnesota Bureau of Criminal Apprehension (BCA) to help investigate an outdoor growing operation in Meadow Brook near Leader, Minn. Hunters had discovered the site, and authorities believed there were multiple sites in the area.

The Meadow Brook Wildlife Management Area is 5,772 acres, according to the Minnesota Department of Natural Resources. It was created in 1979, and is home to deer, bear, wolves and other game.

Authorities found camouflaged tents, clandestine pits with hoses, jet pump instructions, cooking utensils, fertilizer, sleeping bags and other items that indicated people were living or spending considerable time at the sites, the affidavit said.

In September, investigators encountered several men dressed in camouflage who fled on foot and remain at large. They could not be identified. Authorities found 50 to 70 pounds of dried marijuana and about 5,000 plants.

Investigators were alerted in November to a new site 5 miles from the Meadow Brook location. A pill bottle from Regions Hospital was recovered from a garbage pit, and authorities believe it could belong to someone who was responsible for operating and managing the site.

Investigators from the BCA, Cass County Sheriff's Office, the U.S. Drug Enforcement Administration, Homeland Security and the U.S. Forest Service are involved in the case.

The Cass County Sheriff's Office did not return calls seeking comment.

Chao Xiong • 651-735-1762