122 UNIVERSITY OF COLORADO STUDIES 



Hedysarum carnosulum Greene Artemisia jrigida Willd. 



Lupinus flexuosus Lindl. Carduus tracyi Rydb. 



Lupinus greenei A. Nels. Chrysopsis villosa Nutt. 



Anogra coronopifolia (T. & G.) Britton Chrysothamnus afflnus A. Nels. 



Asclepias speciosa Torr. Chrysothamnus glaucus A. Nels. 



Orthocarpus luteus Nutt. Grindelia squarrosa (Pursh) Dunal 



Vegetation of ridges. — Below an altitude of 7,000 feet the ridges are 

 of sedimentary rock, mostly Mesa Verde and Dakota sandstone. The 

 soil is shallow, sandy and rocky except where large exposures of Mancos 

 shale are disintegrating. In many places the strata of the hillsides are 

 exposed and the only soil occupies rock crevices. The tree growth of 

 ridges consists of pinyon pine and Utah cedar (Fig. 11). These two 

 species are always associated. In the vicinity of Newcastle (altitude 

 5,562 feet) cedar forms probably 90 per cent, of the tree growth, pinyon 

 pine being relatively less abundant. At higher altitudes, however, 

 pinyon pine increases in abundance relative to cedar. At the upper 

 altitudinal limit of the pinyon-cedar zone, pinyon pine, not cedar, 

 extends higher. 



These two species are particularly adapted to withstand severe 

 climatic conditions. From the account of climatology it may be seen 

 that the annual ranges of temperature in western Colorado are wide. 

 Diurnal ranges of temperature are also wide there and especially on 

 stony ridges where pinyon pine and cedar grow. These two trees grow 

 in an open stand, occupying a sandy, stony soil and are seldom fifteen 

 feet high. 1 



The common shrubs of ridges are Cercocarpus parvifolius, Amelan- 

 chier spp., Symphoricarpos spp. , Peraphyllum ramosissimum, Fendlera 

 rupicola and Atriplex canescens. Sage-brush and rabbit-brush are 

 scattered. Ephedra antisyphilitica, the joint-fir, was found associated 

 with pinyon pine and cedar in the vicinity of Newcastle, but at no point 

 farther north. This peculiar shrub is more at home in southern Colo- 

 rado, New Mexico and Arizona. Its occurrence at Newcastle is a high- 

 latitude record. 



At this season of the year, the herbaceous vegetation of ridges is 

 sparse, as will be seen from the following list. 



1 Phillips, F. J., "A Study of Pinyon Pine," Bot. Gaz., Vol. XLVIII, pp. 216-23, September, 1909. 



