8 The Colorado Experiment Station. 
• The months of greatest rainfall at the College are April, May, 
June, and July, which with that of the months of March and August, 
makes a total of 10.72 inches out of the total for the year, that falls 
during the growing season and is directly available to growing 
crops and ranges of the State. The rainfall of the State as a whole 
averages about 15 inches annually, the rainy season being in the 
spring and early summer months. The portion falling in the moun¬ 
tainous section is subject to a large run-off, and is gathered by the 
streams for use below, while the run-off on the plains is much 
smaller, being 10 to 15 per cent., but falling on a comparatively flat 
surface the moisture is absorbed by the soil and is directly available 
to the cultivated crops or natural stock range. An accurate knowl¬ 
edge of the rainfall or precipitation of this State is extremely desir¬ 
able. All agricultural activities depend upon the amount and time 
of the year it is available, directly or through the aid of irrigation. 
Colorado, in common with a large part of the Rocky Mountain re¬ 
gion, is occasionally visited by long dry spells. Since the distribu¬ 
tion of pressure which brings about this condition is generally wide¬ 
spread, the dry periods prevail at the same time over extensive areas. 
During the last few years, for instance in 1910, from January 4th to 
April 29th, only 0.28 inches of moisture fell at Fort Collins. In 
1907-08, from October 1st to May 1st, the total precipitation was 
only 0.82 inches, .44 of which fell in one storm in November, but 
fortunately this period was followed by a wet May, 5*^3 inches, 
which was followed by favorable rainfall permitting good crops to 
be secured. 
Absence of precipitation does not always mean drouth, espe¬ 
cially when the soil is moist and evaporation is retarded by cloudi¬ 
ness and unfavorable wind conditions. Therefore, the maximum 
period without rainfall as a measure of the intensity of drouth must 
take into calculation the previous period and these other conditions. 
Then again the maximum period without rainfall often, in fact 
usually, occurs during the non-growing season, the autumn and 
early winter months having little or no effect on crops except that 
we need all the snow we can get on the high mountains for next sea¬ 
son’s supply. There is quite a wide range between the amount of 
precipitation in the wettest and driest years. For the wetter years 
the difference in amount may be two or three times the amount of 
the drier years. The snowfall for the winter months in Colorado 
is small, the average for November and December being the least in 
the year. However, on the crest of the range and on the high moun¬ 
tains, the snowfall is heavier and is stored there, especially in large 
drifts in the timber and gulches and north hillsides, for use in irri¬ 
gation the following season. While many of the streams of the 
State have a good flow during May and June, they fall short during 
