Ignorance of federal laws and the growing influence of legal pot in neighboring states like Colorado has led to an increasing number of Yellowstone National Park prosecutions of visitors possessing small amounts of medical or recreational pot, according to Park rangers.

Marijuana use remains illegal on federal land. The U.S. Attorney’s Office in Cheyenne reports it prosecuted 21 marijuana cases from Yellowstone Park in 2010 and 52 in 2013.

But as of Dec. 17, the case load had grown to 80 in 2014. Those convicted of misdemeanor possession commonly receive a $1,000 fine.

The number or prosecutions are small compared to the millions of visitors who travel each year to Yellowstone Park. Most of the 2.2-million-acre national park is in Wyoming, with portions extending into Montana to the north and Idaho to the east.

Yellowstone Park’s chief ranger, Tim Reid, said he believes the increase in marijuana prosecutions mirrors changes in marijuana use in society.

Alex Freeburg, a criminal defense lawyer in Jackson, Wyo., who frequently handles marijuana possession cases from Yellowstone Park, said his clients often are surprised when they’re charged for small amounts of marijuana.

“They know it’s illegal but they don’t think it’s a crime,” Freeburg said. “There’s some sort of disconnect.”

A typical marijuana case arises from a traffic stop when rangers say they smell marijuana in the vehicle, and many times people tell rangers they have marijuana with them if asked, Freeburg said.

“In which case, there’s not a lot a criminal defense attorney can do for them,” he said.