TOPOGRAPHICAL NOTES. 233 



mountain walnuts and other shrubs, are found in all the mountain ranges. 

 The flats, where not barren sand or gravel, are mostly covered with gamma 

 grass ( Coutelona) of different species, and buffalo grass (Buchloe). Of larger 

 plants, divers cactus species, yucca plants, grease wood, cat claw, and mesquite 

 bushes grow and show a tendency to spread more and more in a westerly 

 direction. In the Rio Grande bottom the tornillo takes the place of the 

 mesquite of the higher land, and the Agava americana, somewhat different 

 from the Mexican species, grows and blooms at nearly every place where the 

 altitude reaches 5000 feet. Of some importance, also, is the Lecheguya, a 

 plant belonging to the Agava family, used by the Mexicans for making ropes 

 and other articles of great strength, which covers large areas along the hill- 

 sides, and is, on account of its dense growth and formidable thorns, a very 

 great obstacle to man and animals in crossing such areas. 



