FOX HILLS AND LOWER MEDICIXE BOW 3 



avcragcs bctwcen 10 and 15 inchcs, little of which falls during thc growing season, 

 which usually lasts from 80 to 110 days in the summer months, June to Septcmher. 

 The mcan annual tcmpcrature is rather low, avcraging from 40 to 45° F. During 

 the short growing season, however, tempcratures of over 100° F. are not unusual. 

 Koppen and Geiger ' place the areas in the Dry, Cold, Steppe climatc, BSKW. 



Ecologically, the vcgetation in thc areas of both southern Wyoming and north- 

 westcrn Colorado may be divided into two distinct units: the sagebrush-grassland 

 association of the dry ridges and divides, and the poplar-willow association of the 

 moist, narrow flood plains of the permanent streams. In the following list of com- 

 mon species, those present in southern W'yoming, but not in northwestern Colorado, 

 are marked with an asterisk (*) ; those in northwestern Colorado, but not southern 

 Wyoming, with a dagger (f) ; the unmarked species are prevalent in both areas.- 



Ridges and Divides (Sagebrush-Grassland Association) : 



Trees and shrubs — 



Artemisia tridentata Nuttall — Black sagebrush 

 Atriplex nuttallii S. Watson — Salt sage 

 Chrysothamnus graveolens (Nuttall) Greene — Rabbit brush 

 Eurotia lanata (Pursh) Moquin — White sage or Winter fat 

 Grayia spinosa (Hooker) Moquin — Hop sage 

 Juniperus spp. — Cedars 

 Kunzia tridontata (Pursh) Sprengel 

 t Pinus eduHs Engelmann — Pinyon pine 

 Sarcobatus vermiculatus (Hooker) Torrey — Greasewood 



Herbs — 



Agropyron spicatum (Pursh) Scribner and Smith — Wheat grass 



Bouteloua ohgostachya Torrey — Short grass 



Bulbilis dactyloides Rafinesque-Schmaltz — Buffalo grass 



Elymus sp.? — Rye grass 



Opuntia spp. — Prickly pears 



Stream Flood Plains (Poplar-Willow Association) ; 



Trees and shrubs — 



Amelanchier alnifolia Nuttall — Service berry 

 Cercocarpus ledifoHus Nuttall — Mountain mahogany 

 t Crataegus rivularis Nuttall — Black haw 

 Populus angustifolia James- — Narrow-Ieaved cottonwood 



* Populus sargentii Dode — Broad-leaved cottonwood 



* Ribes longiflorum Nuttall — Flowering currant 

 Ribes spp. — Gooseberry 



Rosa sp.? — Wild rose 

 t Salix amygdaloides Anderson — Willow 



Salix longifolia Miihlenberg — Willow 



Shepherdia argentea Nuttall — Buffalo berry 

 t Symphoricarpus oreophilus Gray — Waxberry 



' Koppen and Geiger, Klimakarte der Erde (Gotha, Justua Perthes), 1928. 



' Detailed observations on distribution are given in Cary, M., N. A. Fauna, vol. 33, 1911, and vol. 42, 1917. 



