2 BULLETIN 1306, U. S. DEPARTMENT OF AGRICULTUKE 
foothills. A considerable part of this land is irrigated, but much^of 
it is so situated that water for this purpose can not be readily ob- 
tained. Large areas of tillable land also are found in the high land 
away from the streams. In general, the altitude of the farming 
land*^ ranges from 3,400 to 5,000 feet. 
The native vegetation is fairly representative of the area and very 
similar to that found on other portions of the northern Great Plains. 
The more common grasses include buffalo grass (Bulhilis dactyloides) ^ 
blue grama (Bouteloua gracilis), western wheatgrass (Agropyron 
smitJiii), and needle grass (Stijpa comata). Grasses predominate in 
the vegetation, but in addition to them sagebrush (Artemisia spp.), 
many legumes, and other herbaceous plants are found. 
The greater part of the station is on a northeast slope, which is 
fairly uniform. Two small drainage courses passing through the 
land make a small portion of it unsuitable for experimental purposes. 
Narrow strips on the north and east sides are rough and unadapted 
to experimental work. The soil of the southern half of the farm|is 
a dark heavy clay loam with a small quantity of gumbo. That "of 
the northern half is lighter and more friable. 
CLIMATE 
The Sheridan Field Station records of the monthly, seasonal 
(April 1 to August 31), and annual precipitation for the seven years 
from 1917 to 1923, inclusive, together with the averages for that 
period are shown in Table 1.^ Averages also are included for the 
Sheridan station of the United States Weather Bureau for the same 
period and for the 31-year period from 1893 to 1923, inclusive. 
Table 1 also gives the average monthly precipitation at Verona and 
Gillette, Wyo., for April to August, inclusive, for the 7-year period 
from 1917 to 1923, inclusive. This affords a general comparison of 
the rainfall at the experiment station and in the surrounding area 
and shows that the experiments have been conducted under condi- 
tions of rainfall fairly representative of the area. 
Wide fluctuations have occurred both in the quantity of annual 
rainfall and in its distribution during the season. A study of the 
records of rainfall and crop yields shows the distribution of the pre- 
cipitation to be a most important factor with respect to crop production. 
A small amiual rainfall well distributed throughout the growing season 
will often result in better crops than a much larger rainfall poorly dis- 
tributed. The total precipitation in 1920 was comparatively low, but 
the greater part of it was v,^ell distributed during the growing period, 
and the year was one of the best for crops that has been recorded. 
Daily records of the evaporation from a free water surface from 
April 1 to September 30 are made each year. The evaporation is 
dependent upon various factors, including temperature, wind, and 
huniidit}" of the atmosphere, and constitutes a fair index of the cli- 
matic factors other than rainfall influencing crop production. Evap- 
oration tends to vary inversely with the precipitation, and at Sheri- 
dan it has ranged from 1.51 times the precipitation during the same 
period, in 1923, to 8.2 times the precipitation, in 1919. 
The mean temperature from April 1 to Septem.ber 30 averaged 
59.5° F. for the 7-year period from 1917 to 1923, inclusive. Tempera- 
1 The climatic data at the Sheridan Field Station have been obtained in cooperation with the Biophys- 
ical Laboratory of the Bureau of Plant Industry. 
