Are National Parks Becoming Crime Havens?

July 25 -- America's national parks have long been a perfect escape for vacationers, places where families could retreat to a world where the biggest fear was a run-in with a local bear.

Times have changed — and so have the parks. While families camp and boat and enjoy the beautiful wilderness, park rangers are suiting up in camouflage to fight drug dealers, smugglers, and even, on occasion, terrorists.

Watch Chris Cuomo's full report on 20/20 this Friday at 10 p.m.

"Just about any type of crime that goes on in any urban environment happens out here," said Dale Antonich, chief ranger at the Lake Mead National Recreation Area, located in Nevada and Arizona.

"We've had rapes, we've had murders in the park, we've had bodies dumped in the park," Antonich said.

An hour outside of Las Vegas, Lake Mead is one of America's busiest parks. Rangers also considered it to be one of the top 10 most dangerous parks.

At Lake Mead, 36 rangers try to safeguard some 8 million visitors a year, policing more than 1.5 million acres of land, including historic Hoover Dam, and nearly 750 miles of shoreline.

Last year, rangers responded to more than 20,000 incidents — ranging from drunken driving, to boating accidents, to assault, to suicide. Nearly 1,400 were criminal investigations.

20/20 rode along with rangers over the busy Memorial Day weekend. In one instance, they responded to an assault call in which a man, recently on parole after serving time for carjacking, was assaulting his mother. His mother, rangers learned, is a convicted felon times two, for child molestation and kidnapping.

Family Vacation Nightmares

Elsewhere in the park, we and the rangers met the Klasing family, who came to Lake Mead looking for the serenity of nature, but wound up witnessing an ugly scene involving some other campers.

"The woman was screaming, 'You're hurting me,' and the tent was flying all over the place. … Never dreamed we'd run into that. That's why we bring our kids here," said Sue Klasing, describing the incident to the rangers.

The rangers sorted out the domestic disturbance, only to find the troubled family has other problems. They're homeless and had been staying in the park for about a month.

The vacation is one the Klasings will never forget, but not for the right reasons. "This is not how you build family memories," said Bill Klasing.

"You want to be able to come out here and camp at a beach and feel safe and we can't assure that anymore," Antonich said.