CRESTED BUTTE, Colo. -- Rangers in the Grand Mesa, Uncompahgre and Gunnison National Forests said they continue to find marijuana "smoke shacks" on forest land within the boundaries of the Crested Butte Ski Area.

Any shacks that are found are torn down and the builders or users are prosecuted, a forest service spokesman said Friday.

Last December, two Western State College students were issued citations and fined $850 for damaging natural resources and building illegal structures. They were also barred from Crested Butte, as a result, according to a news release.

"The Forest Service is releasing this information to encourage responsible and legal use of the national forest by recreationists," Gunnison District Ranger John Murphy said. "We want folks to enjoy their public lands; however, we also want to let those who do not comply, know that arrests and prosecutions do (and) will occur."

U.S. Forest Service Patrol Captain Dan Nielsen said in February that the rangers found additional smoke shacks.

"It is illegal to construct or maintain any structure on forest service land without special use authorization," he said at the time.

Neilson said that maintaining could be defined as tightening string or wires holding the structure together, or clearing a path to access a structure in the national forest.

Nielsen said inspecting the ski area for illegal structures is a routine procedure.

"We’ve worked with the other resorts and found similar structures," he said.

There have been other infractions on forest lands as well, the forest service said in Friday's news release.

In March, two snowmobilers were observed entering and operating their snowmobiles in the West Elk Wilderness (a posted boundary) and Forest Service law enforcement officers were able to contact the riders as they exited the Wilderness. Both riders were issued citations for a minimum fine of $500 each with a maximum of up to $5000 fine.

Authorities said that in April, four people were found operating a motor vehicle in a restricted area and were in possession of controlled, illegal substance, open container of alcohol and drug paraphernalia. They were cited for multiple infractions including possession of an open container alcohol, illegal possession and operating motorized vehicle in a closed area. One individual had an outstanding warrant for his arrest and was turned over to police.

"Please be aware, that not everyone you encounter on the Forest may be law abiding," Murphy stated. "Recreationists who encounter unlawful activity are encouraged to leave the scene safely and alert the appropriate authorities with any information they may have."