10 



BULLETIN UNITED STATES GEOLOGICAL SURVEY. [FoJ.Vi 



Olneya Tesota, Gray. 

 Farlcinsonia Torreyana, Watson. 

 Frosopis juliflora, DO. 

 JProsopis puhescens, Bentli. 

 Acacia Greggii, Gray. 

 Prunus Fennsylvanica, L. 

 Cercocarptis ledifoUus, Nutt. 

 Fyrus samhucifolia, Cham. & Sclil. 

 Cratcegus — near rivularis, !N"utt. 

 Amelanchier alnifoUa, Nutt. 

 Cereus giga?iteus, Engelm. 

 Samhucus glauca, Nutt. 

 Arbutus 3Ienziesii, Pursh, var. 

 Fraxinus anomala, Torr. 

 Fraxinus pistacicefoUa, Torr. 

 Fraxinus viridis, Miclix., f. 

 Chilopsis saligna, Don. 

 Flatanus Wriglitii, Watson. 

 Juglans Californica, Watson. 

 Juglans riipestris, Engelm. 

 Quercus Fmoryiy Torr. 

 Quercus hypoleuca, Engelm. 

 Quercus undtdata, Torr. 

 Betula occidentalism Hook. 



Fopulus Fremontii, Watson. 

 Fopulus inonilifera, Ait. 

 Fopulus tremuloides, Michx. 

 Fopulus tricliocarpa, Torr. & Gray. 

 Juniperus occidentalis, Hook. 

 Juniperus Californica, Carr. 

 Juniperus Yirginiana^ L. 

 Juniperus pacJiyphlaea, Torr. 

 Ahies concolor, Lindl. 

 Ahies suhalpina, Engelm. 

 Fseudotsuga Fouglasii, Carr. 

 Ficea Fngelmamii, Engelm. 

 Ficea pimgens, Engelm. 

 Larix occidentalis, ^CsTutt. 

 Finns edulis, Engelm. 

 Finus fiexilis, James. 

 Finus aristata, Engelm. 

 Finus Chihuahuana, Engelm. 

 Finns contorta, var. Murrayana, Eng. 

 Finus ononopJiylla, Torr. 

 Finus ponderosa, Doiigi., var. scopu- 



lorum, Engelm. 

 Finns Arizonica, Engelm. 



Yucca hrevifolia, Engelm. 



This mere botanical enumeration of about fifty species of trees, or at 

 least arborescent x)lants, gives no proper idea of the arboreal flora as it 

 presents itself to the view of a botanical traveler. It includes all the 

 trees we know to inhabit any part of a vast tract, extending from the 

 eastern base of the Eocky Mountains to the eastern base of the Siena 

 Nevada and Cascade ranges, and from the Mexican boundary, in kiti- 

 tude 32°, to the northern limit of forest, in about latitude 50°. The 

 characters of the flora at the two extremes are most widely different. 

 There is a far greater development of forest in the northern part, but it 

 consists of the fewest species ; and to the southern portion an undue 

 appearance of richness is given to a very scanty sylva — first, by the enu- 

 meration of so many species which are only arbusculw in their best 

 estate, and are commonly mere shrubs; second, by including species 

 which belong only or mainlj^ to the Mexican frontier region — to the south- 

 ern part of Arizona and ^ew Mexico. 



Of the latter sort are Yucca hrevifolia, the only monocotyledonous arbo- 

 rescent species (tree it cannot well be called) ; the giant Cactus, Cereus 

 giganteus, of the Lower Gila district; Finus Ghihuahuana and P. Arizonica, 

 which barely cross the Mexican line; Sapindus marginatus, Arbutus 

 Menziesii, or what seems to be a mere geographical variety of tlie 

 Californian MadroSa, which is not uncommon in Mexico, and which 

 reaches Southwestern Texas; Fraxinus anomala and F. pistaciafoUa, 



