A guru well known to aficionados of wilderness navigation and mapping visited Folsom on Thursday.

Jeff Caulfield of National Geographic Maps, Inc. hails from Salt Lake City but travels to REI outlets to expound on the virtues and vices for wildernesses trekkers and mountain climbers of global-positioning-system devices.

He spoke Thursday evening at Folsom's REI, on Iron Point Road.

Caulfield's audiences tend to include people who are merely good wilderness travelers who, unlike Caulfield himself, might exhaust their skills at navigating by compass, map and stars and still find themselves lost or stuck.

"I have friends who've gone into places where they didn't understand the terrain, got into a slot canyon and the wall they were trying to climb down was too steep," Caulfield said. "The GPS allowed them to backtrack faithfully through the area they'd come through."

This was in southern Utah, a maze of orange rock.

However, GPS can create a drawback for packers whose energy outdoes their acumen.

"People buy GPS pre-loaded with maps, and think they have all they need," Caulfield said. "But in reality... ."

It's sort of the MapQuest weakness-become-horror-story because you're walking.

Nearby Yosemite Valley gives an example, Caulfield said.

"From Upper Pines Campground to summit Half Dome, GPS would have you walk well more than a mile right up the face of Half Dome," Caulfield said. "So, plan a less direct route — Vernal Falls, Nevada Falls, Little Yosemite Valley, part of the John Muir Trail and then to the summit."

A sense of dead reckoning should only complement quality maps and compasses, skill at using them and knowledge of the astral constellations and how they can guide a traveler. It's the same with GPS technology, Caulfield said.

"GPS is more of a companion (than a substitute) for good map and compass skills," he said. "But, GPS also works in total darkness — fog, or a low cloud layer — and during white-outs."

Advanced trekkers who pride themselves on specific feats can get a lot out of GPS, Caulfield said.

"GPS records where you've been. For example, you're trying to summit a particular peak, but mountains have false summits. Or, you say you hiked the Pacific Trail, but were you on the John Muir Trail instead."

GPS was developed by the U.S. Department of Defense in connection with intercontinental-missile weaponry. Now, it's among the techiest of tech toys.

"It evolved into civilian use," Caulfield said. "For example, you can mark accurately where you parked your car. We now have the benefits of those tax dollars (spent for war)."

The Telegraph's Roger Phelps can be reached at rogerp@gold-

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