APPENDIX SS. 1759 



differentials thereof, of which a prominent one is the southern exposure, and if upon 

 thf surface, like isothermal curves, could run lines of limit to cereal cultivation, the 

 comparison of their elevations upon the opposite sides of the range would be distinctly 

 pronounced in favor of the southern. Beyond this area, where stretch at higher alti- 

 tudes regions fitted for pasturage, an examination of their proper defining lines and 

 above, the limit of arborescent vegetation, better known in the x>atois of the frontier 

 as "timber-line," will be found but an extension of the rule. 



Section IV. — The seasons. 



In this elevated region there are, strictly speaking, two distinctive seasons prevail- 

 ing, the wet and the dry, the former the longer. The long-continued rain-storms ac- 

 companying the advent of the spring months do not obtain here as in the East with the 

 almost daily increment of heat ; in summer and early fall occurs the most frequent pre- 

 cipitation of rain. This varies somewhat, however, with the locality. In North Cen- 

 tral Colorado, September is known, from personal experience, to be the rainy month, 

 affected by proximity to the main range, however ; elsewhere, within 50 miles, the 

 precipitation being much less. The storms generally occur in the afternoon, and from 

 the rarity of the air and the arid state of the atmosphere, within a very brief time 

 thereafter the surcharging of the air with moisture, noticed subsequent to rain-storms 

 in the East, disappears. 



The local variation of rainfall was verified by personal observation and the record 

 kept during the reconnaissance. In June, while along the Conejos, the La Jara, and the 

 Alamosa rivers, and in the Summit mining district, at elevations varying from 7,800 to 

 12,000 feet, the weather was clear and beautiful; no rainfall occurred. 



In July, while along the Conejos, part of the Chama between Tierra Amarilla and 

 Pagosa Springs, along the Blanco, the Piedra, and the Upper Los Pinos to the Rio 

 Grande, it rained almost daily, mainly during the afternoon and evening, three hail- 

 storms being met with. 



During the prevalence of this season, as is well known, the precipitation upon the 

 mountain-tops is greater than below, storms there being frequently seen, while lower 

 localities escaped. At Pagosa Springs, 7,084 feet (a supply camp), most beautiful sun- 

 sets were observed and exemption from storms was had, while they could be seen not 

 many miles distant. 



In August, while ascending and descending the San Juan and tributaries to as low 

 as 7,000 feet in the Summit district, along the upper Rio Blanco, and the Navajo, the 

 Chama, the Nutria, the Piedra, and the Los Pinos, we encountered twelve storms of 

 rain, with four of hail, the heaviest met with during the trip, and the most severe 

 being near the summits of the mountains. Several times marches were made through 

 heavy storms to valleys of less altitude which had escaped, as was found the month 

 before. 



In September, the region traversed was the Upper Los Pinos, the Vallecito and trib- 

 utaries (where snow-storms were encountered), both upper and lower parts of the same 

 the Florida, the Animas to the San Juan and vicinity, the La Plata, the Mancos, the 

 Dolores, and the Grand Canon of the Animas to Silverton and Howardsville. In all 

 these marches but six rain-storms (two of them with hail) were met with, chiefly in 

 the mountains. All were in the first portion of September, heavy frosts occurring 

 daily after the early part of the month. 



In Ocober, the sections passed over included the Lake City region and vicinity, the 

 Rio Grande, including its South Fork, the Summit district, and Del Norte, the entire 

 canon of the Rio Alamosa, the Conejos, &c, during which but two rain-storms, with 

 six severe snow-storms, of extended area were encountered, the localities of all being 

 near the mountain summits or upon elevated plateaus. 



From the above it will be seen that most of the rainy days were in July and part of 

 August, and from the middle of the former for about a month the greatest precipita- 

 tion was met with. None befell us anywhere in August after the 18th and scarcely 

 any in September ; in October, those occurring were but exceptional ones, till the win- 

 ter's inclement season began with heavy snows in the mountains. 



One of the oldest settlers upon the Animas, who came into our camp at Pagosa 

 Springs, volunteered the information that the rains in the lower San Juan travel west- 

 ward in a regular manner; that is, that the rainy season commences earlier and ceases 

 sooner in the eastern portion of this region than in the western ; that when over at 

 the Chama and the Navajo, they still prevail upon the Los Pinos and the Animas ; in 

 short, that had we begun in the latter country and worked to the east, this disagreeable 

 feature of outdoor life in the mountains would have been escaped. Whether, as he 

 insinuated, it would be possible for the traveler to commence at the west and passing 

 east to avoid all of the storm limit save at the point of passage must remain a matter 

 of conjecture. It is simply mentioned for the benefit of those hereafter in a like 

 situation. 



