South Dakota Geological Survey. 



Plate 4 



The Prickly Pear (Opuntia polyacantha\ especially abundant on 



Grai 

 ground. 



the flats or benches along the valleys. Grama grass in back- 



Snow-on- the- Mountain (Euphorbia marginata] abundant on 

 steppe. 



Chrysothamnus graveolens. A conspicuous plains composite. 



