Il6 UNIVERSITY OF COLORADO STUDIES 



this was xerophytic. Rocky ridges with scattered pinyon pines and 

 cedars; stream benches, level areas, roadsides, gradual slopes and 

 mesas covered with sage-brush; scrub oak at the bases of slopes; stream- 

 sides fringed with cottonwoods; a dearth of blooming herbs — such was 

 the general appearance of the country. 



After three weeks of sage-brush and stony ridges an aspen grove was 

 a relief. It was an indication of moister and cooler climatic conditions 

 and a greater variety of plant species. Aspens become abundant at 

 7,000 feet altitude. A very few Rocky Mountain yellow pines (rock 



Fig. 6.— Generalized N-S cross-section in vicinity of Little Beaver Creek. Sage- 

 brush covers the lower portions of the long, gradual slope from Little Beaver Creek. As 

 the soil becomes more shallow at the upper part of the slope, sage is replaced by scattered 

 clumps of oak. Pinyon pine and cedars occupy the steep, rocky south exposure. The 

 north slope covered with dense oak chaparral is steeper than the slope from Little Beaver 

 Creek, and hence sage-brush is confined to a narrow strip along the stream. 



pines) are scattered among them. At this elevation Douglas and blue 

 spruce occur in moist, shaded gulches. At about 8,000 feet altitude 

 lodgepole pine appears in abundant numbers, and at about 10,000 feet 

 Engelmann spruce forms the dominant tree growth, extending up to 

 timberline. Aspen is far more abundant in northwestern Colorado 

 than at similar altitudes on the eastern slope. It is usually much larger 

 also, often reaching a diameter of two or more feet and with bark at the 

 base of the trunk corrugated. 



The greater time of the expedition was spent at altitudes below 

 7,500 feet. Furthermore, in making comparisons between the flora and 

 vegetation east and west of the continental divide, the differences are 

 particularly marked at the lower altitudes. For the above reasons this 

 account will be restricted for the most part to a discussion of conditions 

 existing below an altitude of 7,500 feet. 



