Why does this happen so often on the left coast?

Quite a few years ago, when GPSs first became popular, DH and I were on a business trip in Socorro, NM. After dinner, we decided to go for a drive to watch the sunset. We saw a side road that went into BLM land and up onto a hill. So we went and enjoyed the sunset. We were kind of clueless as to how to get back so we used the GPS. 4 hours later, we found ourselves in a field of longhorn steer. It was pitch black, but we did manage to see a sign on a fence, "Entering New Mexico Institute of Mining and Technology Bombing Range." It took us another hour to get back to hard surface road (15 minutes to push through the cows alone)and back to the hotel. I have never trusted a GPS again and carry detailed paper maps of any area we travel.