1842 REPORT OF THE CHIEF OF ENGINEERS. 



"with several species of Atriplex, but upon the western slope Artemisia tridentata, Pursh, 

 often accompanies them, forming almost impenetrable thickets. 



A prominent feature of the western slope is the great extent of country covered by 

 the " sage-bush," A. tridentata, and nearly impassable, excepting by the trails which 

 run through it. These ' ' sage-bush " plains are not found upon the eastern slope, the 

 so-called " sage-bush" plains being parks with Sarcobatus, Atriplex, and Bigelovia, and 

 other smaller shrubby plants, growing upon them. 



The mesa slopes of the Avest are more thickly covered with shrubs, than upon the 

 eastern Rocky Mountain slope. The southern species and those from the. Interior 

 Basin are so common, that they form the most striking part of the vegetation. Cerco- 

 carpusparvifolius, Nutt., and Amelanchier alnifolia, T. & G., are found upon both the east- 

 ern and western slopes, but upon the western Amelanchier is much more abundant. 

 The very common bushes of the western San Juan region are Purshia tridentata DC, 

 Cowania Mexican a, Don., Peraphyllnm ramosissimnm, Nutt., Fendlera rupieola, Eng. & 

 Gray, and Ephedra trifurca, Torr. 



The Mesa Verde, a large mesa of the western slope, is covered with Juniperus occi- 

 dentals, Hook., intermingled with some Finn* edulis, Eng., and Juniperus Virginiana, L.; 

 and upon its western edge Fraxinns anomala, Torr., Glossopetalon spinescens, Gray, and 

 Coleogyne ramosissima, Nutt., are often found. 



Yucca angustifolia, Pursh, grows upon both the Atlantic and Pacific slopes, but T. 

 baccata, Torr., is plenty only upon the western slope. The genera Astragalus and Eri- 

 ogonum are represented mainly by different species on the two sides of the mountains. 

 A. lonchocarpus, T. & G., E. microthecwni, Nutt., E. Jamesii, Benth.,i£. umbellatum, Torr., 

 E. cernuum, Nutt., are common upon both slopes. 



The conspicuous smaller plants of the western mesas, in place of the common Pent- 

 stemons, Aplopappi, Bigelovias, Townsendias of the eastern slope, are Pentstemon linari- 

 oides, Gray, Aplopappus Nultallii, T. & G., A. armerioides, Nutt., Solidago pumila, Bigeloria 

 Wrightii, Gray, B. depressa, Gray, Hosackia Wriglitii, Gray, Actinella Torreyana, Gray,* &c. 

 The species of Loasacese, Solanacea?, and Nyctaginaceae, well represented in the Rio 

 Grande Valley, are equally so in the San Juan Valley. 



Until both eastern and western slopes are thoroughly explored, it is only negative 

 evidence that a plant has not been found upon either slope, but what is known makes it 

 certain that there is a decided change from the flora of the eastern slope on the Los 

 Pinos, Animas, La Plata, Man cos, and Dolores Rivers. 



CHAPTER VIL— ENTOMOLOGY: 

 PREFATORY. 



Touching the botanical collection mentioned in the previous chapter, the precursory 

 remarks there made are also applicable here. 



While the time essential for any comparatively full representation of the insect- 

 fauna was not available, an attempt was made to obtain as large a number as possible 

 of the Articulata to aid investigators in defining the range-limits of their specialties ; 

 particular attention being paid to the Lepidoptera, Coleoptera, Neuroptera, mxd the Acri- 

 didce of the Ortlioptera. 



Traveling mainly with pack-train, some of the collections were unfortunately lost 

 through accidents in the field and in transit, including a valuable collection of Neurop- 

 tera, which Dr. H. Hagen, the eminent naturalist in charge of the Museum of Com- 

 parative Zoology of Harvard University, Cambridge, Mass., had promised to classify 

 and report upon. 



The collection of Ortlioptera was expressed to Prof. Cyrus Thomas, of the United 

 States Entomological Commission, whose classification and report, as Section I, will be 

 found hereafter. For his kindness and the unrewarded time and labor devoted thereto 

 we desire to express our sincere thanks. 



The largest and most difficult collection of any specialty, several hundred Lepidoptera, 

 comprising both Bhopalocei'a and Heterocera, were sent for classification and report to 

 Prof. Herman Strecker, of Reading, Pa., whose private collection, numbering over 

 60,000, is the largest in the world. In addition thereto over 600 specimens of a gener.il 

 collection of Articulata were expressed to Mr. Strecker for the same purposes. Both 

 classification and report, involving an immense amount of time and labor, have been 

 promised gratis, and we desire to tender him onr thanks therefor. At the time of leav- 

 ing the office to take the field, it had not yet been received, but its completion is prom- 

 ised at an early day, and in time for publication. 



