LIFE ZONES OF CARLSBAD REGION 15 



vegetation, may still afford a fair haven for a few 

 plants that can break its crust or utilize or avoid its 

 mineral content. Thus we have areas of infinite mix- 

 ture of plants and again areas of almost pure stands, 

 called plant associations. We may ride for miles 

 through a golden mantle of flowering creosote bush on 

 gravelly slopes, or fragrant fields of varnish bush on 

 the floor of the valley, or through areas of solid tobasa 

 grass in the path of occasionally flooded bottoms, or 

 among the blazing torches of ocotilla on the steepest, 

 hottest, and dryest slopes,- — an endless variety of 

 plant associations, each full of meaning and of vital 

 significance to the student of plant ecology. 



The Upper Austral zone, or its Upper Sonoran arid 

 division, in the Carlsbad Cave region, begins at about 

 the level of the cave entrance, or 4,500 feet on gentle 

 south slopes, but on northerly slopes it begins as low as 

 4,000 feet and extends up over the high mesas and foot- 

 hill ridges of the Guadalupe Mountains to 7,000 or 

 8,000 feet, according to slope exposure. On steeper 

 slopes these limits are somewhat extended, and on very 

 gentle slopes correspondingly less extreme, while such 

 minor factors as barrenness, color and nature of soil, 

 moisture and air currents, show slightly modifying 

 effects on zone levels. 



In the immediate vicinity of the great cave, as over 

 much of this zone, its most striking feature is a scattered 

 growth of scrubby juniper, striking because the un- 

 mistakable dark evergreen bunches may be seen and 

 recognized miles away. In the rough ridge and foot- 

 hill country they practically fill the zone, but are absent 



