Pool : THE VEGETATION OF THE SANDHILLS OF NEBRASKA 239 



of the region which reveal the greatest numbers of such depressions 

 there are extensive stretches of the hills covered so effectively with 

 vegetation that blow-outs are seldom seen. The unmistakable evi- 

 dences of former wind action are, however, present in abundance in 

 such areas. The most universal indices of former conditions are 

 seen in the configuration of the hills and ridges and^n the presence 

 of blow-out relicts. 



Regions of present maximum blow-out conditions are found 

 between the Middle Loup and Dismal rivers in Thomas and Hooker 

 counties, and in the lake district above the headwaters of Blue Creek 

 in Garden County. In certain places the ranges of hills are little 

 else than ranges of blow-outs of various ages. At one place near 

 the Dismal River I counted sixty-eight blow-outs within an area of 

 approximately one square mile. These were large active blow-outs 

 ranging in size from 20 to 75 feet deep and from 35 to 150 feet in 

 diameter. In addition to this number there were many smaller 

 embryonic blow-outs in this same area, and still others that had 

 reached a late stage in vegetative stabilization. On the other hand 

 there are hundreds of square miles, as in Cherry and Holt counties, 

 that show few or no blow-outs. Even in such comparatively blow- 

 out-less areas, however, one occasionally finds enormous blow-outs 

 upon the highest hills or ridges in the neighborhood. 



Composition of the Blow-Out Association 

 dominant species 

 Calamovilfa longifolia Redfieldia flexuosa 



Psoralea lanceolata 



PRINCIPAL SPECIES 



Cristatella jamesii Pentstemon haydeni 



Eragrostis trichodes Phaca longifolia 



Eriocoma cuspidata Polanisia trachysperma 

 Muhlenhergia pungens 



SECONDARY SPECIES (invaders) 



Anogra cinerea Hymenopappus Mifolius 



Asdepias arenaria Lathyrus ornatus incanus 



Chrysopsis villosa Lygodesmia juncea 



Cyperus schweinitzii Meriolix serrulata 



Eriogonum annuum Prunus besseyi 



Euphorbia petaloidea Rumex venosus 



Froelichia Uoridana Sideranthus spinulosus 



