92 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



most timber, the west side being rocky and precipitous. At the sum- 

 mit Populus tremuloides and Que reus gambelii form a distinct forest 

 zone, below which Pseudotsuga mucronata and Pinus strobiformis 

 grow luxuriantly, and arc bounded below by a zone of Pinus ponde- 

 rosa, the base being wooded as in the San Luis Range. 



The presence or absence of forests in this region depends upon the 

 amount of moisture in the ground. This is illustrated by the accom- 

 panying diagram (fig. 2), showing the distribution of trees on the 

 west side of the Animas Mountains. Below the timber line is a 

 barren slope, several miles in extent, at the foot of which is a chain 

 of springs, below these is a belt of fine oak timber {Quercus emoryi 

 and Q. arizonica) which derives moisture from the springs just above 

 them. The diagram also shows the downward prolongation of tim- 

 ber in moist canyons. This is especially noticeable in passing across 



Animas Peak 



Bottom of Animas Valley 



Fig. 2. — Distribution of trees on the west side of the Animas Mountains. 



San Luis Pass, which corresponds to the zone of Quercus emoryi and 

 Quercus arizonica, to a broad valley east of the mountains, from 

 which many lines of oak trees are seen extending down ravines from 

 canyons in the San Luis Mountains; and in one instance a straggling 

 line of oaks actually becomes continuous across the valley, joining 

 one from a canyon in a mountain range to the eastward. 



Station No. 20. — San Luis Springs, Grant Count}', New Mexico. 

 This is at present better known as Lang's Ranch, a famous camping 

 place for Government troops in pursuit of hostile Indians. The 

 springs, which are unfailing, are close to the Boundary at Monument 

 No. 66, just below timber line of the western foot of the San Luis 

 Mountains, and on the eastern edge of the broad Animas Valley. 

 (Plate X, fig. 1.) Altitude, 1,57? meters (T>,174 feet) at Monu- 

 ment No. 66. Game was abundant, and water and grazing good. 

 On a preliminary reconnoissance in advance of the surveying parties, 

 conducted by Lieut. I). I). Gaillard, commissioner, accompanied by 

 the present writer and Lieut. Francis G. Irwin, camp was made at 



