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GPS accuracy/Summit measurements/Four Corners

February 13 2008 at 1:30 PM
Lynn Arave  (Login LynnArave)


I have three related outdoor inquiries — 1. Relating to GPS accuracy, 2. Where summit elevations are measured from; and 3. The location of the true "Four Corners."

1. When I climbed Humphrey's Peak last September, my Garmin GPS was off by about 15 feet from the posted 12,633 elevation of Arizona's highest summit. I can't recall if it was high or low, but it was off.
My GPS readings often also seem to oscillate back and forth by 10 or so feet on its readings almost continually.
Have others found similar discrepancies? Are higher end GPS devices more accurate?
My GPS saves me from any disappointments regarding false summits when I hike, but it's never exact on its readings it seems.
I believe the display on my GPS even says accuracy to within so many feet at times.
Obviously when I'm holding my GPS at chest level, it is 3 or so feet higher than the ground.

2. Hikers always pile up rocks on peaks like Kings and Humphrey's for shelters or to make it higher, but I've always assumed the peak's listed elevation is from the ground, not piled up rocks. Is that right? (Of course all of Kings Peak seems to be loose rocks...)

3. When I visited the Four Corners monument (Utah-Arizona-Colorado-New Mexico common point) 3 years ago, I didn't have my GPS along. Since then I see occasional references to the actual Four corners being hundreds of feet or yards away to the west.
Has anyone ever checked the accuracy of the Four Corners monument? It may be where it is because of access and flat ground and not true accuracy..
Also, when I checked my GPS against the location of the Utah-Arizona border near Littlefield a few years ago, my GPS said the actual stateline was about 80 feet south of where the border's sign and marker were. So, it's not just elevation my GPS varies on, but coordinates too.
Maybe these are more geocaching questions, but I still wonder.
Jack Parsell in his Tri State Corners book never seemed to question the location of markers, like at Four Corners .......

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