Like NM, Colorado has calichi (sp) mud. Slick as snot when wet, balls up and when it dries it is like cement. Mix a little grass or straw with it and you make adobes. Our gun range has the clay, it will build you boots up to 10 pounds pretty quick
When I lived in Arizona, I had to do some digging for work. Easy with a shovel, until we hit that caliche! It was like cement.
