Just about every week for three years, Tom Rabenhorst ventured into Patapsco Valley State Park with a 4-foot-tall, red-and-white striped pole topped with a circular antenna.
The 58-year-old geography teacher and his wife, Carol, 57, tackled switchback trails and rock formations, tracking their progress with a Global Positioning System unit and doing something that had never been done.
They mapped all 170 miles of trails in the sprawling park.
"It's a monumental feat without a doubt," said Lt. Chris Bushman, the park manager. Park officials had long hoped to produce maps that might enable hikers to explore the more obscure trails, he noted.
"What Tom did by volunteering his time and expertise was to move us along a lot faster."
The state bought the rights to the map and paid for printing costs. The maps are on sale at the park and online for $6.
For Tom Rabenhorst, mapping the park was a chance to combine his favorite hobby with his professional expertise.
He and his wife are geography teachers at the University of Maryland, Baltimore County and Carroll Community College. And they love to hike. Together, the Finksburg residents have explored parks in all but two states on foot.
Barring heavy rain or illness, they hike four to five miles every weekend. Even when the trail is solid ice, they press on, stepping off the trail and crunching the ice where they must.
This summer, Carol Rabenhorst and the couple's three grown sons went on a three-week vacation in Montana's Glacier National Park. The couple is now exploring the Caledonia state park in Pennsylvania, west of Gettysburg, where they ended up bushwhacking their way to the Appalachian Trail.
"For five hours, we saw no one. That's what we love to do, find an old trail and see where it goes," said Carol Rabenhorst. "You feel like you can unwind on a trail. You get addicted to it."
After more than 25 years of marriage, they are compatible hikers, enjoying silent contemplation as well as long talks. Now they want to share that experience with others.
"People know Patapsco exists, but they see it as a lot of trees. It may be scary, but this map clears up all the mysteries and makes it more inviting," Carol Rabenhorst said. "Most of the fun is seeing things for the first time. It's the geographer in me. I want to know what's around the next boulder, the next bend."
That sense of adventure led them to take it upon themselves to map Patapsco Valley State Park, no small endeavor.
It's a place that stretches 30 miles long from tip to toe -- about 14,500 acres, according to park officials -- and crosses into four counties: Carroll, Howard, Baltimore and Anne Arundel.
It was easier for them to map in the late fall and winter, when the leaves weren't on the trees to block the satellite reception. The striped survey rod with the antenna fit into Tom Rabenhorst's belt holster. The antenna was connected to the GPS device in his hand.
They downloaded the GPS data onto a computer, and the software transformed the information into map format. They used a graphics program to fine-tune the images.
After producing their first draft, the Rabenhorsts walked all the trails again to double-check their calculations.
The map folds out to cover most of a small desk, with half the park on one side and the other half on the other.
The color-coded topographical layout designates mileage markers, streams, camping areas and scenic vistas.
On both sides of the map, color snapshots taken with Carol Rabenhorst's digital camera capture the park's diversity -- ruins of old homes, tunnels, giant ferns, riding trails and attractions such as Swinging Bridge and the Lost Lake.
The pictures document their all-season treks and portray the park as a place that can be enjoyed in shorts and T-shirts as well as with cross-country skis.
They believe the map will probably appeal to more adventurous hikers interested in reaching the park's more remote areas. The map is sold at park offices, contact stations and online at www.trailmapsetc.com. About half of the initial printing of 5,000 copies have been sold this summer.
Officials at the state Department of Natural Resources, who had never found the money to commission a map, considered the Rabenhorsts' offer a relative bargain, said Bushman, the park manager.
"For the GPS work alone, it's $200 a mile, based on contracts the state is getting now," Bushman said. "So it'd be $34,000 right there, without another round to double-check the results."
But the Rabenhorsts sold the rights for $6,000.
And their mapmaking days aren't over. At the request of state natural resources officials, they are hiking -- and mapping -- Gunpowder Falls State Park.