Notes on Forest Conditions in Northwestern Nebraska 53 



and south canyons with many laterals the steep sides of which 

 arc talus slopes formed from the crumbling rocks of the Ari- 

 karee formation, and covered with a scattered stand of 

 I'hnix ponderosa. 



Three great types or formations of plants may readily be 

 distinguished throughout this area as it occurs in Sioux county. 

 These formations are primarily determined by topography and 

 cdaphic conditions. 



The Ridge and Butte formation is seen covering the more 

 or less level and linear, or broad and irregular table-lands at 

 the tops of many of the ridges and buttes that have persisted 

 as the canyons have been cut through the great escarpment. 

 This is the least forested formation of the three since the soil 

 conditions and vegetative characters are very similar to those 

 relations typical of the High Plains to the south. In fact 

 this is merely the grassy formation of the High Plains which 

 has been cut and dissected by erosion and has then persisted 

 as narrow tongues, isolated areas at the tops of buttes, or 

 broader plateaus when the most of the surrounding surface 

 has receded under the action of the eroding forces that hol- 

 lowed out the canyons from the rocks of the Arikaree. These 

 areas often connect with the main grass formation which ap- 

 proaches the escarpment from the south. In some places they 

 become more or less wooded and extend entirely through the 

 region to the northern or lower side of the escarpment. 

 Naturally then this formation is seen in its best development 

 toward the upper or southern portion of the region where the 

 canyons head and where the divides are relatively broad. 



The soil here is thin and light and inclined to be more 

 rocky than farther back in the main body of grassland that 

 covers the High Plains. A very thin layer of darker soil with 

 a little humus often covers the surface over small areas. Out- 

 crops of the Arikaree formation are common along the upper 

 portions of the canyons while deeper down these rocks form 

 the rims or irregular margins of this plant formation. 



The vegetation of the ridges and buttes is characterized 

 by the presence of many species of plains plants, especially 

 of the grasses and legumes. An<!r<>[><>gon scoparius, Stipa 

 conKita, Kocleria cristata, and Agropyron tenenun are the 

 dominant grass species. Besides these grasses which make 



