Ive been hunting right along the Nevada California State line and ended up buying a non-resident California Hunting License because I had no idea when in the field where the state line was. I bought a Garmin GPS because the salesman told me that it would show me where the state line was withing about 12 feet. When out in the field with the GPS I was more confused than ever. One minute the California State line was .5 miles to the West next time the Nevada State line was .5 miles to the East. I called Garmin and explained what I was doing and was told that the GPS was good to about .5 miles. I called again and another rep told me the same thing. I even stood right on the State line on a paved road and It was still .5 miles off.........................I took it back and now rely only on 7.5 minute maps and just to protect myself bought the California Non-Resident License.
I can't believe anyone at the company would give you that .5 mile BS! Nobody would be using a GPS if they were not accurate and the salesman gave you the right poop on them. Most of the time, especially if you have WAAS activated on the units, they are accurate within 15'. I can't tell you how many corner posts and surveyor markers I've found with mine because they are that accurate. I have no idea why the state line boundary would have been showing like you stated on yours and if it was also screwing up on the highway location you should have gone to where you bought it and exchanged it for another because they are better than sliced bread. If you get the land ownership chips for them, you actually can completely eliminate the need for a paper map.
Yes, GPS with WAAS enabled will be accurate to within feet. No problem there.
But, the problem is with the accuracy of the loaded features. What the Garmin reps were saying is the accuracy of the features in the map are only accurate to .5 miles. They are simply not positioned correctly everywhere. I'd be willing to bet that they are tied to fixed locations at regular intervals. The further you are from one of these location ties, the more error you will see.
Well, I had the cheapest Garmin they made $118 It seems a lot simpler to just buy the Non Resident Hunting License. I was trapping on the state line but after loosing Traps to thieve. I'm heading further back into the Mountains on the Nevada Side....................................IN my opinion its best to stay as far away from California as Possible...........................