The reason ALL GPS manufactories state: DO not use the GPS ONLY for navigation.

From Fox News:

PORTLAND, Ore. In a holiday hurry, Jeramie Griffin piled his family into the car and asked his new GPS for the quickest way from his home in the Willamette Valley across the Cascade Range. It said he could shave 40 minutes off the time of the roundabout route he usually takes to the in-laws' place.
Following the directions, he and his wife headed east on Christmas Eve and into the mountains, turning off a state highway onto local roads and finally getting stuck in the snow.
They had no cell phone service and ran short on formula for their 11-month-old daughter. After taking exploratory hikes, trying to dig out and spending the night in their car, the distraught couple filmed a goodbye video.
Like two other parties of holiday travelers who followed GPS directions smack into Oregon snowbanks, Griffin and family were eventually rescued. But their peril left law enforcement officers and travel advisers perplexed about drivers who occasionally set aside common sense when their GPS systems suggest a shortcut.
"Did everybody just get these for Christmas?" asked Klamath County Sheriff Tim Evinger, leader of one rescue effort.
In Griffin's case, in fact, the GPS device was a Christmas gift, from his parents. He used it for the first time to plan the trip to Central Oregon.
It's one he'd made many times before, following a route travelers have found reliable since at least the days of the Oregon Trail. But, he said, a shortcut the GPS device suggested was attractive.
"We were in such a hurry to get over there, we programmed it in the driveway and went ahead," he said.
In hindsight, he said, he should have double checked the route against a paper map and packed extra formula for the baby. "We would be better prepared for the unknown," he said.
The AAA and the National Association for Search and Rescue say they don't sense a surge in trips that go amiss because of a blind reliance on GPS directions, but they hear about them from time to time.
"It's usually about every other month," said Christie Hyde of the national travel association AAA. It's a small number compared with the millions of GPS units in service, she said.
She's heard, she said, of one driver who made a right turn as directed and had to be towed off railroad tracks, and another party led near the edge of a cliff.
In Oregon, GPS systems can direct drivers to thousands of miles of Forest Service logging roads that lace the state's mountain ranges. In the winter, they are often plugged with snow.
On Christmas Day, a Nevada couple took one such road in Evinger's County and spent three days stuck. They were rescued when a break in atmospheric conditions allowed them to signal their coordinates to 911.
Three Portlanders and their small dog got into trouble Monday when their vehicle slid off a forest road as they were using GPS directions to a hot springs in the southern Willamette Valley. Lane County officials said the three and the dog were exhausted and mildly hypothermic after walking 17 miles without survival gear to get into cell phone range and call 911.
Griffin's family was rescued when friends and relatives used a GPS like Griffin's and duplicated the route they assumed the family had plotted. That led them straight to the family. The three had been stuck about 24 hours.
Evinger recalled that within the last year in his county a hunter in a pickup followed GPS instructions along a powerline road and got stuck in a marsh, and travelers in a car got stuck in snow when they turned onto a Forest Service road that had been closed and converted to use for snowmobiles.
But, he said, it isn't as if people have just started getting lost in the woods. "In yesteryear, it was people not knowing how to read their maps," he said.
Evinger said the statewide task force on search and rescue he chairs will take up the question of GPS-led trips next week. He said it probably would focus on educational efforts rather than legislation.
Law enforcement officials and travel experts have a variety of recommendations for people who use GPS in the winter or in strange territory:
Use an old-fashioned paper map as a backup. Pack a survival kit for the winter. Configure your GPS for "highways only," or a similar setting, so that you don't get directed to byways in the winter. Top off your gasoline tank, and charge your cell phone batteries before going into remote areas. Pay attention to the weather.
"Our devices don't know what the weather is," said Jessica Myers, spokeswoman for GPS manufacturer Garmin. "It's the responsibility of the driver to exercise common sense."
Several officials recommended zooming out from GPS displays that focus on the stretch ahead. A wider view can point to better highways for a safer, if lengthier, drive. It can also jog a driver's mindset by offering a "full, bird's-eye view of the area around you," said Marie Dodds, spokeswoman for the AAA's Oregon and Idaho organization.
The most common advice was high in "duh" content:
"You can't follow GPS blindly," said Hyde of the national AAA.
Says Dodds: "If you are following your GPS and all of a sudden you find yourself in the middle of nowhere with snow all around, don't go there. Turn around."

SPOT Rescue Alert: Injured Hiker Rescued from Canadian Rockies After Sending GPS Coordinates and Distress Message from his SPOT Satellite Messenger

MILPITAS, CA (September 23, 2008) SPOT Rescue Alert (SRA): On August 22, 2008 experienced hiker and Canadian oil analyst Michael Ervin, set off to enjoy a backcountry wilderness trip to the base of Mount Assiniboine, one of the highest and most distinctive peaks in the Canadian Rockies outside of Banff. A bad fall under the weight of his forty-five pound backpack left Mr. Ervin with a ruptured quadriceps tendon to his knee, unable to put any weight on his leg and 10 kilometers from the nearest road with no cell phone coverage.
I heard a loud snap from my leg and could see my knee cap hanging loose, lower than usual, said Michael Ervin, President of fuel-analysis firm MJ Ervin & Associates of Calgary. I was experiencing shock and knew I was unable to walk. I needed real help and pressed the 9-1-1 button on my SPOT Satellite Messenger to notify emergency responders of my GPS location coordinates.

The SPOT Satellite Messenger is a personal safety device which enables users to communicate via satellite technology from remote locations around the globe and initiate check-in and emergency response calls independently of cellular networks.

Banff National Parks, which maintains a 24/7 rescue office, immediately dispatched a local Parks helicopter to Mr. Ervinís exact location. He was flown to Banff Mineral Springs Hospital and underwent surgery the next day.

As a pilot, I learned about SPOT through my membership with COPA (Canadian Owners and Pilots Association) and purchased the device because it was more affordable than other PLBs and due to its GPS location capability SPOT is far more reliable than the 121.5 ELT, added Mr. Ervin. Because it is small and lightweight, I take SPOT with me on my backpacking trips to stay connected with my family and friends at home. This time, it proved vital in getting me the quick medical attention that I needed.

Mr. Ervin is no stranger to this wilderness area. This was his third attempt of reaching the base of Mount Assiniboine by foot along the 29 Kilometer Citadel Pass Trail. His previous attempts were never completed due to a forest fire one year and inclement weather brought on by an early winter storm during a later attempt.

This is but a speed bump on the highway of life, and after I have completed my recovery in the next few months I will try to make it back to Mount Assiniboine.