16 American Midland Naturalist Monograph No. 4 



of the channel as the Colorado River cuts its way through layers of sand- 

 stone, limestone, and shale, is from 4 to 18 miles across and over a mile 

 deep. Precipitation varies with the elevation as does the vegetation cover. 

 The yearly average on the North Rim (8,000 to 9,000 feet) is 27 inches, 17 

 inches on the South Rim (6,500 to 7,500 feet), and 7 inches in the bottom 

 of the canyon (1,850 to 2,500 feet). 



The forest on the South Rim is predominantly pifion-juniper (Pinus 

 edulis and Juniperus utahensis) , but there is some ponderosa pine (Pinus 

 ponderosa) to the east and Douglas fir (Pseudotsuga taxijolia) occurs in 

 shaded places just below the rim. Because the forests are open, shrubby growth 

 is common and the number of species considerable. A few of the more 

 characteristic shrubs are cliffbush (Cowania Stansburiana) , Gambel oak 

 (Quercus Ganibeh), desert serviceberry (Amelanchier Covillei) , Utah service- 

 berry [Amelanchier utahensis), mountain mahogany (Cercocarpus montanus 

 and C. intricatus), Apacheplume (Fallugia paradoxa) , and big sagebrush 

 {Artemisia tridentata) . Sagebrush often occurs in association with fourwing 

 saltbush (Atriplex canescens) , green ephedra (Ephedra viridis), grasses, and 

 herbaceous plants. 



Many of the above-listed species are common also on the canyon walls 

 below the South Rim and down nearly to the Tonto platform. In addition 

 there are many others worthy of note, including fendlera (Fendlera rupicola), 

 snowberry (Symphoricarpos rotundifoiius and vS". longiflorus) , hoptree (Ptelea 

 Baldwini), singleleaf ash (Fraxinus anomala), mock-orange (Philadelphus 

 microphyllus) , and Nevada ephedra (Ephedra nevadensis) . Southwestern 

 fragrant ash (Fraxinus cuspidata var. macropetala) is very showy during the 

 flowering season along the Bright Angel trail in the redwall limestone forma- 

 tion. It occurs also in the same formation below the North Rim. 



The North Rim forest on the Kaibab Plateau is predominantly ponderosa 

 pine along with white fir (Abies concolor) and Colorado blue spruce (Picea 

 pun gen s) . Aspen is also very common, occurring either in pure groves or 

 intermingled with the conifers. Characteristic shrubs found in openings or 

 along the edges of the forest are western locust (Robinia luxurians) , moun- 

 tain common juniper (Juniperus communis var. saxatilis), and greenleaf man- 

 zanita (Arctostaphylos patula) . CliflFrose is also abundant on some of the 

 open points near the edge of the rim, such as at Cape Royal and Point 

 Sublime. 



Below the rim in more or less sheltered or shaded canyons may be found 

 forests of white fir and Douglas fir. Associated with them are often found 

 redbud (Cercis occidentalis) , bigtooth maple (Acer grandidentatum), Rocky 

 Mountain maple (Acer glabrto7i) , ceanothus (Ceanothus Martini), New 

 Mexican raspberry (Rubus deliciosus var. neomexicanus) , and smooth rock- 

 spiraea (Holodiscus discolor var. glabrescens) . 



■ On the Tonto platform may be found a desert type of vegetation, tree- 

 less except perhaps for a few small broadleaf trees along streams, and for the 

 most part sparsely covered with low straggly shrubs adapted to withstand 

 severe drought. A few of the many species include blackbrush (Coleogyne 



