SCIENTIFIC EXPEDITION TO NORTHWESTERN COLORADO 121 



typical of rocky slopes On north slopes sage-brush often grades into 

 scrub oak (Fig. 6). The sage-brush formation forms a pure, close, 

 regular stand In any sage-plain the shrubs are of uniform height, 

 commonly three or four feet (Fig. 8). Along roadsides and in more 

 favorable situations, however, individual plants may reach a height of 

 six to eight feet. 



Rabbit-brush {Chrysothamnus sp.) is the common associate of sage- 

 brush It occupies moister soil, being found nearer to streams and in 

 places where seepage exists. Looking over a sage-plain, the silvery- 

 gray sage-brush is readily distinguished from the greener rabbit-brush. 

 Grease-wood alternates with sage-brush in alkaline soil. 



It is not uncommon to find low, rounded hills covered with large 

 patches of vegetation which give them a yellowish hue This color is 

 due to an association of Chrysothamnus glaucus, Eriogonum cam- 

 panulatum and Gutierrezia sarothrae, all with yellow bloom. This 

 association is a common one of the sage-brush formation. 



Sage-brush has a great altitudinal range and will grow under a 

 variety of edaphic conditions. As has been said, it is best developed 

 below 6,000 feet altitude over flat areas, having rather deep, fine-grained 

 soil. It is by no means absent, however, from steep slopes; it often 

 forms there the undergrowth below piny on pine and cedar. Sage- 

 brush decreases in abundance with altitude, but occurs at times as high 

 as 10,000 feet. At high altitudes it is confined to warm, exposed ridge 

 crests. 



Sage-brush alternates with oak chaparral on north and south slopes. 

 The north exposure may be clothed with oak shrubbery while the south 

 exposure bears sage-brush, the two formations meeting at the bottom of 

 the gulch. 



In northwestern Colorado, the present farming land occupies, almost 

 without exception, areas which were covered with sage-brush. This 

 has been removed by "grubbing." 



Collection of Plants from Sage-Brush Formation 



A triplex confertifolia S. Wats. Salsola tragus L. 



Erigeron campanulatum Nutt. Sarcobatus vermiculatus (Hook.) Torr. 



Grayia brandegei Gray Astragalus haydenianus Gray 



