206 BULLETIN UNITED STATES GEOLOGICAL SUKVEY. [Vol.Yl. 



as to be visible from any elevated point of observation, this being due 

 to the characteristic coloration of the foliage of plants composing the 

 zones. Frequently, however, the limit of growth of plants or trees 

 upon a mountain slope can only be approximately ascertained by ob- 

 serving the altitude where the representatives of two zones ax)pear to 

 be about equal, and either way from which point the species of one or 

 the other will begin to predominate in greater number to the exclusion 

 of the other. This is the case upon the mountains in the southern por- 

 tion of the State; the lower line of the zone of Conifer cb is represented 

 chiefly by the nut-pine [Pinus monophyllus) and the western cedar {Juni- 

 perus occidentalis) which, resting upon the upper edge of the zone of 

 Salicacice, marks the line below which the Piiion Jay ( GymnoJcitta cyano 

 cephala) is seldom found, while in the lower zone we find the Eobin 

 {Merula migratoria propinqiia), Hammond's Flycatcher {Umpidonax liam- 

 mondi), and Gairdner's Woodpecker (Pieus pubescens gairdneri), which 

 may be considered peculiar to that zone and seldom ascending into the 

 one above it. In addition to the species just named as characteristic 

 of, or generally resorting to, the Coni/erce, are Sialia arctica^ Lanivireo 

 solitarius plumheus, and Lanius ludovicianus excubitorides. 



Although the zone of Salicacice is readily determined, representatives 

 of it diverge to either side along the the mountain canons where there 

 is moisture, and sometimes away out into the adjacent plain. The more 

 common species of trees composing the zone proper, as well as the 

 branches which follow the water-courses, are the willows, cottonwood, 

 and aspen ; and some of the more prominent species of birds frequenting 

 them in greater or less number are Dendrceca cestiva, Geothlypis trichas, 

 Tachycineta bicolor, Passerina amoena, Icterus bullocM, Asio americanus, 

 Tinnunculus sparverius, &c. These represent only a few of the constant 

 summer visitors to this wide-reaching zone, but they are confined to cer- 

 tain elevations and genera of trees composing the zone with more char- 

 acteristic persistency than most any other species which I had the op- 

 portunity to note. 



Upon the plains in Northern Nevada, where the sage-brush (Artemisia 

 tridentata) predominates, the characteristic species are Oreoscoptes mon- 

 tanus, Spisella breiceri, Plialcenoptilus nuttali, Centrocercus urophasianus, 

 and most promiaently so AmpMspiza nevadensis. In the southern inte- 

 rior of the State 0. montanus, P. nuttali, and G. uropliasianus were found 

 in the same belt of vegetation, which had risen to an elevation of over 

 8,000 feet, while in the former region the same vegetation occurs mainly 

 below 6,000 feet. 



In the zone of vegetation below the Artemisice, which appears in con- 

 sequence of the elevation of the latter in the southern part of the State, 

 we detect in regular order Yucca baccata, Y. angustifolia, Cacti of vari- 

 ous sub-genera, and toward the deserts Uriodictlon, Algarobia, and Pro- 

 sop is. Amongst the latter, especially in the regions east, northeast, and 

 north of Fort Mojave, the avi fauna is that of the Colorado Valley 



