HERPETOLOGY OF ZUNI MOUNTAINS — GEHLBACH 247 



Section continues into the San Juan Basin. On tlie south the Zunis 

 and North Plains of the Datil Section are replaced by the San Augus- 

 tine Plains and rugged montane highlands associated with the Basin 

 and Range physiographic province. 



East of the Zuni Mountains, Mount Taylor, an 11,389 foot Miocene 

 volcano, dominates the area of eroded, basalt-capped mesas known 

 collectively as the San Mateo Mountains (not to be confused with an 

 uplift of the same name in Socorro County). Mesa Chivato is the 

 northeastern extension of this highland mass, which is approximately 

 15 by 35 miles in extent. Its slopes are drained by the Rio San Jose 

 and Chico Arroyo and drop to 5794 feet at Laguna on the eastern 

 end of the study area. This is about the southeastern boundary of 

 the Colorado Plateau as marked by the westernmost faults of the 

 Rio Grande (Hunt, 1956, p. 6). 



Extensive lava beds or malpais, derived in part from Mount Taylor, 

 are most conspicuous south of Grants. They stretch 30 miles on a 

 southwesterl3^-northeasterly axis and are surrounded by a relatively 

 flat plain several feet lower than the overrun lava. Cinder cones 

 border the main malpais, which ranges from 8308 feet at the top of 

 Flagpole Crater to 6200 feet near McCarte3^s. Much soil has ac- 

 cumulated where the lava is relatively smooth, as in the vicinity of 

 El Morro National Monument and Cebolleta Mesa. This basalt is 

 probably of late Miocene origin, whereas rough, broken malpais along 

 the Rio San Jose near Grants is of Pleistocene derivation (Hunt, 1956, 

 pp. 46, 53). The McCarteys lava may be less than 1200 3^ears old 

 (Nichols, 1946, p. 1049). North of Bluewater another small malpais 

 lies isolated on the Cretaceous plain and, near it, numerous volcanic 

 necks stud the landscape. 



Climate 



The Zunis are characterized by a semiarid-mesothermal climatic 

 regime with a P-E Index of 16-32 (Thorn thwaite, 1931). It may be 

 seen that local moisture conditions are allied closely with elevation 

 and exposure (fig. 2). Prevailing air currents are southwesterly. 

 Below 8000 feet average annual precipitation values are 13 inches on 

 the southwest and 10 on the northeast; above 8000 feet, 20 inches is 

 the average annual value (U.S. Dept. Comm., 1945-1957). The 

 period of greatest rainfall occurs from July through September. 

 Short, heavy thundershowers are then common and often result in 

 flash floods. Heavy winter snows usually are limited to the elevations 

 above 8000 feet. 



Pearson (1931, table 14) has assembled annual mean precipitation 

 data for various plant zones in Arizona and New Mexico. They 

 range from 11 inches in the grasslands and 16 in pinyon-juniper 



