196 



THE DESERT 



of agate and carnelian. The mesas themselves 

 are made up of sand and gravel, sometimes 

 long shelvings of horizontal rocks, sometimes 

 patches of terra-cotta, rifts of copper shale, 

 or beds of parti-colored clay. 



There is more rain in this upland country 

 and consequently more vegetation than down 

 below. Grease-wood grows everywhere and is 

 the principal green thing in sight. So pre- 

 dominant is it that the term "grease-wood 

 plains" is not inappropriate to the whole re- 

 gion. Groves of sahuaro stand in the valleys 

 and reach up and over the mountain-tops, 

 chollas and nopals are on the flats ; the mes- 

 quite grows in miniature forests. But besides 

 these there are bushes and trees not seen in the 

 basin. Palo fierro, palo bianco, cottonwood 

 live along the dry river-beds, white and black 

 sage on the mesas, white and black oaks in the 

 foot-hills. Then, too, there are patches of pale 

 yellow sun-dried grass covering many acres, 

 great beds of evening primrose, and fields cov- 

 ered with the purple salt-bush. It is quite an- 

 other country when you come to examine it 

 piece by piece. 



As you rise higher and higher to the Conti- 

 nental Divide the whole face of the mesa under- 



