22 BULLETIN 1333, U. S. DEPARTMENT OF AGRICULTURE. 



dropping rapidly to the west. It represents a region that once, in 

 all probability, bore a heavy forest of Douglas fir, of which only a 

 few relics remain. The lodgepole pine forest winch now clothes the 

 slopes is, for the most part, young and vigorous. No particular 

 study has been made of this locality. The temperature data for the 

 station are introduced simply to show that the temperature conditions 

 conducive to a successful invasion by lodgepole pine are quite uniform 

 throughout the range of the species in this region. 



P-l: Southern Colorado western yellow pine. — Elevation, 7,108 feet; 

 nearly flat river valley. Although the pine forest has been almost com- 

 pletely removed irom the vicinity of Pagosa Springs, this station may 

 still represent in a fair way the temperature and moisture conditions 

 favorable to the optimum growth of yellow pine in southern Colorado. 

 (See PI. VIII, fig. 2.) A valley forest about 20 miles from Pagosa 

 is typical of the forest found here. This type is distinctly not the 

 mesa type so characteristic of Arizona and New Mexico. It is a 

 hilly type in which the best development is reached only on the moister 

 ground along stream courses, and the strongly sloping hillsides. 

 The conditions of this region approach those of Arizona in the amount 

 of the winter precipitation, but at corresponding elevations the 

 Colorado type is deficient both in snow and in the volume of the 

 summer rains. It is probably for this reason that the higher, nearly 

 level ground corresponding to the mesas of Arizona bears onty a 

 meager stand of pine. 



W-Al: Wagon Wheel Gap north slope Douglas fir. — Elevation, 

 9,610 feet; aspect, north; slope, 40 per cent. Tins station is one of a 

 series which has been very carefully and consistently operated since 

 1910, in connection with the stream-flow study conducted by the 

 Forest Service and the Weather Bureau. The meteorological records 

 are of the highest order, although it lias not been possible to reach 

 some of the more inaccessible stations for daily observations. The 

 equipment of this station, as of Stations W-D and W-G, has been 

 about as complete as possible. There was, however, no sunshine 

 record, no recording apparatus for anemometer, nor any record of 

 evaporation until August, 1919. 



The site represented is a steep north slope bearing in general a 

 Douglas fir stand badly damaged by fire some 25 years ago, and here 

 and there replaced by aspen. (See PI. IX, fig. 1.) About the instru- 

 ment shelter there is a fairly dense stand of firs about 40 feet high, 

 but the anemometer and rain gages have been exposed in an opening 

 a few rods to the west where there is an almost bare rock-slide about 

 half an acre in extent. In some places the reproduction is about 

 equally of spruce and of fir, but in general at this elevation the spruce is 

 not of sufficient weight to warrant calling the site a. fir-spruce type. 

 On the whole, the struggle between spruce and fir is in almost the 

 same stage as at the corresponding station at Fremont, F-9. 



In every respect except that of wind velocity, the records of this 

 station agree so closely with those of W-Bl, similarly situated on 

 another drainage area one mile north, that the statement of condi- 

 tions at the latter point would mean sheer duplication. This simi- 

 larity gives further assurance that the records fairly represent the 

 type. 



The equipment of this station has bees maintained essentially in 

 the same status since September, 1910, and is as follows: 



