The cliffs -- steep sandstone and clay -- rise up from the north side of the creek. At the top, a pine forest extends to the fence separating the brick factory's land from Pioneers Park. Well-worn trails run through it all, and all of it is on private property.

"I've been here since 1978, and people have been going back there before that," said Dave Allder, southwest supervisor for the Lincoln Parks and Recreation Department.

Yankee Hill Brick employees have found trash and old clothing and campfire remnants. They've dismantled shacks. They've posted no-trespassing signs all along the fence.

Slaven tells them to not approach trespassers, to instead call the sheriff. "If they're willing to cross a boundary line or jump a fence or whatever, you don't know what they might be capable of."

The plant's call-the-cops policy is designed to protect his employees and his equipment. But, it's more than that, he said.

"It's really a dangerous place to be. You could get hurt back there."

In September 2008, Dustin Jeune and his friends spent a string of nights partying at the cliffs. They would drink beer, sit by a fire and maybe smoke a little pot, one friend said later.