Matt Christian approaches a tree, stepping over a narrow creek carefully. He reaches into a hollow opening facing away from the path and pulls out a sealed Tupperware box. Leaning against the tree, he opens the container and empties out a broken watch and a stubby pen to record his find.

When he’s done signing the logbook he seals the container and slides it back into the opening. “Ninety billion dollars to find Tupperware in the woods!” he chuckles, referring to the high-tech satellite system that makes the sport possible.

Christian, 32, is a veteran of the growing sport of geocaching-where hikers seek out hidden boxes or 'caches' using GPS. An eager public quickly created a game to use this new technology. Individuals or organizations hide caches all over the world. Players submit locations online. A volunteer reviewer checks cache locations and uploads the coordinates to an Internet bulletin board. Players then track down the coordinates to find the cache, signing a physical log at the site and marking their success on the web.

Christian enjoys seeking caches out in the woods, but in the last few years there’s been a move away from traditional wilderness caches, while urban micro caches have become more popular. And as the technology has gone mainstream, the sport has attracted more families and retirees, he said.

Geocaching has sometimes caught flack from conservationists who say geocachers trample endangered plants or disregard park rules. But Christian treads lightly, covering a found geocache with leaves and bark and staying close to the trail.

Geocaching took off six years ago when selective availability was cut off. The accuracy of GPS technology improved tenfold after the government permitted civilian access to 24 satellites around the globe. A boon to navigation, civilian use is purposely less accurate than the same systems used by the military to guide weapons systems.

In the beginning, brushes between geocachers and land managers weren’t always pleasant, and rumors of ‘cachers violating park policies, trampling plants, and burying items were not unusual. This left a bad taste in the mouths of many land managers.

“It was under the radar and people were hiding things all over the place,” admits Matt Busch, who reviews cache locations for geocaching.com. Since then geocaching has gone mainstream, Busch said.

According to Bambi Teague, the Blue Ridge Parkway’s Chief of Resource Management and Science, caches have been found on the Blue Ridge Parkway, even after they clamped down on the sport several years ago. Teague has stumbled over caches herself in the past three years.

On one occasion a cache was hidden in a hole in rattlesnake territory. “You could put a cache down in a place like that and really get yourself into trouble,” she says. Worse still, another cache was found on Rattlesnake Lodge, which has the highest volume of rattlesnakes in the entire park.

“I consider that dangerous or uninformed or both,” she says. In another instance, ‘cachers placed a find in a restricted area with endangered species. “They were trampling these rare species to get to their caches,” Teague said.

Teague said the sport is subject to two national regulations, and land managers treat caches as abandonment of property that pose a risk to natural or cultural resources.

According to Christian, however, ‘cachers aren’t allowed to desert their caches. If you hide a cache, you are responsible for it. This means travelers cannot set up caches while on vacation unless a local ‘cacher “adopts” a cache and promises to maintain it.

“We rely on the common sense of the cacher,” says geocacher Graeme McGufficke.

“There are some basic rules, but on the other hand someone who is local to an area probably has a better idea of what’s going on than some company in Seattle [where geocaching.com is located]. They’re not going to be sending people over to North Carolina to check each cache,” he says.

“We keep the caches off restricted areas like national parks or state parks. If it is in one of those places we query the ‘cacher to see if they have the proper permits,” Busch said. If things don’t check out, reviewers e-mail the ‘cacher and ask he or she to relocate the cache and resubmit it when it’s ready.

“People know each other in their geographic region,” McGufficke says, adding that it is not uncommon to meet other geocachers while hunting for a find. ‘Cachers also gather for events and “Cache In Trash Out” (CITO) get-togethers, where ‘cachers pick up trash.

Sometimes friends begin ‘caching together. Carole Hoekenga, 67, was looking for an activity to do with her friends a year ago, when she started geocaching. Since then the retired educator has racked up 250 caches.

“For me it’s an ideal time in my life to find something like this. It forces me to get out and exercise and I meet new people. I don’t even think of the items in the cache,” Hoekenga says, adding that most of the time the challenge is the reward.

Many caches include riddles, wordplay or other mental challenges. Hoekenga has been on caches that lead her to underground tunnels, conduits and mountain tops.

“I’ve gotten to see so many awesome spots traveling around,” McGufficke says. “Geocaching has shown me places I’d never know about if I’d stayed on the regular local tour.”

“If you want it to be about racing around at a fanatic pace to find caches hidden behind guardrails, you can do that. You can also go for a five-mile hike and find only one cache but have an awesome afternoon, too.”

Four hours and two caches later, we approach the trailhead. We have crossed three creeks, a river where a bridge was washed out, and crisscrossed through Wagon Road Gap. Christian bends over and picks up a piece of trash-remnants of someone’s discarded coffee cup-and says, “Every cache is worth it in its own way.”