You come upon them every now and then -- a mystery of ugliness. What is it? How on earth did it get there? Why doesn't someone get rid of it? We attempt to shed light through this occasional Page Three feature.

The trail dips south from Accotink Park, crosses Pohick Creek, then winds through new subdivisions in Lorton. The city is far away. The crunch of sneakers on asphalt is the loudest sound.

This is the 38-mile Cross County Trail, which opened to Fairfax County in May with a day-long celebration of ribbon-cuttings and fun runs. It's the pride of local politicians, who are reveling in their gift to constituents -- a public amenity befitting the W&OD trail tucked into the suburban sprawl. The trail stitched together a patchwork of old paths and spiffed them up. "Bluebells and Bluebirds in a Utopia of Green," proclaims the Web site of the county Park Authority, describing a "unique and glorious achievement for one American county." A "natural wonderland" achieved with a $4 million investment.

But what's this at mile 36? Markers direct bikers and hikers to two padlocked, rusted gates across the path -- shimmying and portaging around them is required to stay on the path.

Then a sign: "No Trespassing Under Penalty of Law." But the brown trail markers continue, so the journey continues. Until another pair of gates in 40 feet, with another sign: "Government Property, Do Not Enter, Restricted Area." More gates, more signs. Less communing with nature. More markers, although the trail by now is a rutted stretch of asphalt broken by tufts of grass.

The old Lorton prison's hulking form comes into view to the right, where bulldozers are grading the land for a retirement community. The turn-of-the-century prison buildings eventually will be restored.

Park workers tore down the signs two weeks ago after an inquiry from The Post about access to the trail. The signs and gates were security devices to make sure unauthorized cars didn't drive onto the prison property, explained Park Authority spokeswoman Judy Pederson. "Some of those buildings are hazardous," she said. "We consider it an absolute safety issue to not have people wander off that trail."

The signs had preceded the Cross County Trail. "Leaving up those signs was a bit of haste on our part just to get the thing open," she said.

In two months, the awkward gates will be replaced by less intrusive bollards.

Oh, but there will have to be some new signs. They'll clear up any confusion, Pederson said. Something like, "You're On the Trail and You're Allowed to be On the Trail."

-- Lisa Rein