12* - .* . THE BiOLOG^ OF HARDING COUNTY 



The streams are all highly irregular in their flow, except a 

 few spring fed brooks in forested buttes. The chief rivers are 

 (i) the Little Missouri which crosses the northwestern corner in 

 a deep valley along which badland areas and sandy stretches occur. 

 This river system at present drains but a very small per cent, of 

 the county. (2) Most of the area is drained by the south fork 

 of the Grand river and its tributaries. (3) The southern border 

 of the area is drained by the north fork of the Moreau river. 



Numerous classes of soils are represented in this area. There 

 are large, highly sandy belts, smaller, clay ("gumbo") areas and 

 all gradition between these. Most of the area is overlaid with 

 loams. 



The climate is severe. The average rainfall is but little over 

 15 inches, but is very irregular in its distribution. Normally about 

 four-fifths is received in the growing season. The interval be- 

 tween killing frosts in spring and fall averages about 120 days, 

 but the frostless season between the latest recorded spring and 

 the earliest recorded fall killing frost is less than three months. 

 A moderate wind (10 to 12- miles an hour) is normal. It in- 

 creases in velocity during the day, but often dies down at night. 



The vegetation is mostly that of the dry prairies or steppe 

 short grasses and herbs. Groves of trees, chiefly cottonwoods, are 

 found in the Little Missouri valley. In and about the larger 

 buttes are areas which are more or less forested with pine, ash, 

 and cedar. The larger buttes have been incorporated into the 

 Sioux National Forest. 



For a detailed discussion of the topography, geology, soil, 

 climate and mineral resources of this area, see a forthcoming bul- 

 letin (Number 8) of the South Dakota Geological Survey. 



The Biology of the Past. Very early this region of course was 

 without life. At the time represented by the oldest formations 

 known in this definite area life was already abundant. There were 

 woods containing trees (oak, cottonwood, pines, etc.) similar to those 

 of the present. The flowering herbs of that time are unknown. 

 Quite likely these were not yet extensively developed. There were 

 various reptiles, some resembling gigantic "horned toads" with 

 similar armor-plating. Others resembled monstrous lizards, while 

 many were very different from anything now living. For example 



