Bailey &. Bailey: Woody Plants of National Parks 15 



ZioN National Park 



Zion National Park includes a considerable area surrounding Zion Canyon 

 which has been cut by the Virgin River into the Markagunt Plateau in south- 

 western Utah. Elevations range from about 3,700 feet in the valley to about 

 7,800 feet on the plateau. Precipitation averages about 15 inches annually 

 at the lower elevations. 



The canyon is marked by massive sandstone walls, either barren or with 

 a very sparse vegetation cover. Species characteristic of the hot dry talus 

 slopes are scrubby pinons, including both singleleaf pirions (Pinus mono- 

 phylla) and the two-needle pirion {Pinus edulis), Utah juniper (Juniperus 

 lUahensis), and a numiber of scraggly shrubs. Among these may be found 

 scrub oak {Quercus undidata) , mesquite (Prosopis glandulosa) , western locust 

 {Robinia luxiiriaTis) , mountain mahogany (Cercocarpus montanus), narrow- 

 leaf yucca (Yucca angiistissima) , Spanish bayonet (Yucca baccata), skunk- 

 bush sumac (Rhus tnlobata) , and rubber rabbitbrush (C. naus^osus var. 

 graveolens) . Also common on dry flats or slopes or along the roadsides are 

 such species as cliffrose (Cowania Stansbunana) , bitterbrush (Purshia tr't- 

 dentata) , serviceberry (Aynelanchier alnifoHa and A. Covillei), Apacheplume 

 (Fallugia paradoxa), and Gambel oak (Quercus Gambeli), particularly on 

 north-facing slopes. On some of the lower dry washes, such as Coalpits Wash, 

 may be found such desert species as cottonthorn (Tetradymia spinosa), pale 

 desert-thorn (Lycium pallidum), blackbrush (Coleogyne ramostsstina) , four- 

 wing saltbush (Atriplex canescens), snakeweed (Gutierrez'a sarothrae), and 

 rabbitbrush (Chrysothamnus) . 



The valley floors, wherever there are permanent streams, are lined with 

 broadleaf trees such as Fremont cottonwood (Popidus Frenionti), willows 

 (Salix laevigata and S. Gooddingt), boxelder (Acer negundo var. interior), 

 desert ash (Fraxinus veluiina var. coriacea) , and thickets of sandbar willow 

 (Salix exigua) . Around springs on the slopes bigtooth maple (Acer grandi- 

 dentatujn) is common along with desert ash and boxelder. 



On the plateaus ponderosa pine (Pinus ponderosa) is the dominant tree 

 over the higher parts to the north and east. Piiion-juniper is also common 

 in certain areas where Rocky Mountain red cedar (Juniperus scopulorum) 

 occurs along with Utah juniper and piiion. In openings in the forest may 

 be found shrubby species such as thickets of Rocky Mountain white oak 

 (Q^uercus utahensis) or Gambei oak (Quercus Gambeli), serviceberry 

 (Amelanchier alnijolia), snowberry (Symphoricarpos rotundifolius) , blue- 

 berry elder (Sambucus coerulea) , greenleaf manzanita (Arctostaphylos pat- 

 ula), mountain mahogany (Cercocarpus montanus) , big sagebrush (Artemisia 

 tridentata) , and species of currant (Ribes) . 



Grand Canyon National Park 



Grand Canyon National Park in northwestern Arizona includes within 

 its boundaries a section of the Colorado River 105 miles long together with 

 a pKjrtion of the Kaibab Plateau on the north and a section of the Coconino 

 Plateau on the south. The wide chasm, formed by weathering of the walls 



