Sue - reason for that is because most of Colorado is either granite (mountains) or sand (plains). We have very little "dirt" here. Our growing soil isn't very good as this area is too windy for loam or black dirt. And what isn't sand is hard clay. That's why the roads are being washed away as fast as they are .. Nothing underneath them to really hold everything down. In my own yard, I have "soil" (clay) for exactly 12", then it's almost 100% pure sand underneath.
