MAMMALS OF THE MEXICAN BOUNDARY. 47 



the head of Cajon Bouito Creek, in the San Luis Mountains, west to 

 tiie Santa Cruz Valley. The lowest point was in Sonora, near the 

 junction of Cajon Creek with the San Bernardino River (altitude 

 3,199 feet, or !)T.') meters) ; the highest, near, the head of Babocomeri 

 Creek, in Arizona (altitude 5,320 feet, or 1,621 meters). 



SALIX LASIOLEPIS Bentham. 

 BIGELOW WILLOW. 



This willow is abundant on the Pacific slope of the Coast "Range 

 Mountains, in California and Lower California. To the eastward 

 we obtained it only on the Huachuca Mountains, Arizona. 



SALIX NUTTALLII Sargent. 

 NUTTALL WILLOW. 



This is an alpine species, growing near the summits of the Mogollon 

 and San Francisco mountains, in central Arizona, and on San Jose 

 Mountain, in Sonora, Mexico." 



POPULUS TREMULOIDES Michaux. 

 ASPEN; aUAKING ASP, 



Aspens were found only on the summits of the Animas, San Jose, 

 and Huachuca mountains, where they belong to the highest or Boreal 

 zone, and are associated with Quercus chrysolepis, Q. gambeln, Pinws 

 strohiformis^ and Pseudotsuga inucronata. Its vertical range, on the 

 Mexican Line, is from 1,343 meters or 7,690 feet (San Jose Mountain 

 Sonora, Mexico) to 2,887 meters or 9,472 feet (summit of Huachuca 

 Mountains, Arizona). The largest aspens were those on the Hua- 

 chuca peaks^ but none of those seen on the Mexican Line were com- 

 parable in size with the aspens of northeastern Arizona. At Little 

 Spring, at the north base of San Francisco Mountain, Arizona (alti- 

 tude 2,500 meters or 8,250 feet), I measured an aspen that was 1.72 

 meters (5.64 feet) in circumference and 21.3 meters (70 feet) in 

 height. 



POPULUS ANGUSTIFOLIA James. 

 NARROWLEAF COTTONWOOD. 



This handsome cottonwood was collected at one or two places in 

 Grant County, New Mexico, in the vicinity of springs, where it may 

 Iiave been artificially planted. It is a common tree in Tonto Basin, 

 Arizona. I had previously collected it on Fossil, Corduroy, and Car- 

 riza creeks, in central Arizona. 



"Another willow, which I am unable to determine, is abundant in moist 

 valleys near the summit of the Coast Range, in California. This is a scrubby 

 tree from 2 to 6 meters (6 to 20 feet) in height. 



