Eddie Leroy Anderson of Craigmont, Idaho, is a retired logger, a former science teacher and now a federal criminal thanks to his arrowhead-collecting hobby.

In 2009, Mr. Anderson loaned his son some tools to dig for arrowheads near a favorite campground of theirs. Unfortunately, they were on federal land. Authorities "notified me to get a lawyer and a damn good one," Mr. Anderson recalls.

There is no evidence the Andersons intended to break the law, or even knew the law existed, according to court records and interviews. But the law, the Archaeological Resources Protection Act of 1979, doesn't require criminal intent and makes it a felony punishable by up to two years in prison to attempt to take artifacts off federal land without a permit.

Faced with that reality, the two men, who didn't find arrowheads that day, pleaded guilty to a misdemeanor and got a year's probation and a $1,500 penalty each. "We kind of wonder why it got took to the level that it did," says Mr. Anderson, 68 years old.

Wendy Olson, the U.S. Attorney for Idaho, said the men were on an archeological site that was 13,000 years old. "Folks do need to pay attention to where they are," she said.