Imagine being able to drive an all-terrain vehicle right up next to a sacred earthen Native American burial mound.

At Effigy Mounds National Monument, you can. Three million dollars' worth of illegal construction projects went on for a decade at one of the nation's most sacred Native American burial grounds in northeast Iowa. And it happened under the watch of the National Park Service.

The park didn't do the proper archeological studies before installing an intricate boardwalk system that now encircles ancient burial mounds that are shaped like bears and birds.

"I will not rest the rest of my days until all this junk is removed," says Tim Mason, who used to work among these ancient Native American mounds.

Ask Mason his title and this is what you get: "Tree-hugging, dirt-worshipping, hell-raiser."

Mason grew up here. He's now retired, but for 19 years he held a lot of different jobs at the monument, from laborer to park ranger. During visits to the park after retiring, he'd see these boardwalks and other structures going in. Mason filed a complaint that sparked a criminal investigation by a Park Service special agent.

"They had collaborators at every level in the regional office and the national office, and they were securing funds, they weren't doing the checks," he says. "They were violating federal and state law to build all this junk."