570 



NATURALIST'S GUIDE TO THE AMERICAS 



4. NEW MEXICO 



By a. O. Weese 



i. general features and 

 original biota 



1. Physiographic regions 



a. Great Plains. Included in this 

 region is approximately the eastern 

 third of the state. The most important 

 subdivision is the valley of the Pecos 

 river which drains southward into the 

 Rio Grande. 



b. The Southern Rockies extend into 

 the north central portion of the State 

 from Colorado, and continue as some- 

 what isolated chains southward into 

 western Texas. 



c. The Rio Grande Valley, which cuts 

 through the state from north to south, 

 is generally placed, with a small area 

 in the southwestern corner drained by 

 the Gila and its tributaries, in the 

 "Basin and Range" province. 



d. The Colorado Plateau occupies that 

 part of the western half of the state not 

 included above. Mount Taylor, with 

 its associated lava-capped mesas, is the 

 most conspicuous elevation in this 

 region. 



2. Geographic and local plant and 

 animal communities 



The greater part of the state is char- 

 acterized by a temperate grassland 

 broken by rocks, ravines, high and low 

 mountains, etc. The second largest 

 area is eastern succulent semi-desert 

 in the south central part and Pecos 

 valley. There are also considerable 

 areas of xerophytic coniferous forest 

 and of mountain coniferous forest. 



a. Grassland. For plant communities 

 see under Texas (page 507) and Arizona 

 (page 565). 



Characteristic animals are the prong- 

 horn antelope, the coyote and the 

 prairie dog. The bison also, at one 

 time, ranged over the greater part of 

 this area. There are many local varia- 

 tions due to mountains and edaphic 



conditions, such as the presence of 

 streams, playas, saline areas and rock 

 outcroppings. 



h. Eastern succulent semi-desert. See 

 under Texas (page 109). 



c. Forests. About one-fifth of the 

 state is covered with forest, i.e., in the 

 Southern Rockies and the higher parts 

 of the Colorado Plateau. These for- 

 ests, except along water-courses, are 

 of the semi-desert coniferous type, 

 becoming increasingly mesophytic with 

 increasing altitude. 



For xerophytic coniferous forest see 

 under Arizona (page 565) and for moun- 

 tain conifer see under Colorado (page 

 524). 



d. Cross section. A typical transect 

 from Rio Grande Valley regions to the 

 top of an adjacent peak of the Rocky 

 Mountains would show a series of com- 

 munities about as follows: 



(a) River Valley Communities 



1. Mud-flat. Tiger beetle (Ci- 



cindela hirticollis) 



2. Cottonwood forest — Juncus 



meadow savanna. Tiger bee- 

 tle (Cicindela vulgaris), west- 

 ern meadow lark. 



3. Bigelovia association. Blister 



beetle {Cysteodemus wis- 

 lizeni). 



(b) Semi-desert ("mesa") formation. 



Pronghorn antelope, coyote, 

 prairie-dog, desert horned lark, 

 beetles (Eleodiini). 



(c) Cedar (Juniperus monosperma). 

 Western diamondback rattler {Crotalus 

 a. atrox) and collared lizard (Crotaphytus 

 collaris haileyi), 



(d) Pinyon (Pinus edulis) The fence 

 Uzard{Sceloporus undulatus) jPinyon jay . 



(^) Yellow pine (Pinus ponder osa), 

 Black bear, mule deer, band-tailed 

 pigeon. 



(/) Douglas fir {Pseudotsuga mucro- 

 naia). Lynx, dusky grouse, elk. 



{g) Engelmann spruce {Picea en- 

 gelmannii). 



(h) Alpine meadow and chaparral 

 associations. Bighorn sheep (also in g), 

 white-tailed ptarmigan. 



