The New International Encyclopædia…
“ The State is as a whole a treeless prairie country. Forests are found only in the Black Hills above an altitude of 4000 feet, where there is a good growth of pine. Here and there along the river valleys there are more or less extensive groves of cottonwood, ash, elm, and maple. Geology. Although the geological structure of the State is nearly homogeneous over the greater part of its area, there is nevertheless found represented every age from the Archæan to the Pleistocene except the Devonian. There are two Archæan nuclei, one in the east and one in the west. ”
