Why does this happen so often on the left coast?

Last winter I was working at Fort Irwin, an Army base in the dead center of the Calif desert, nearest town is 40 miles away and there is one road in and out. I turned on the GPS as I was going to take a trip to AZ and it kept telling me to turn left on roads that were nothing but dirt and when I looked at a map, went no where except they happened to go east. I learned then and there never to trust a GPS and verify when I do