8 
The Colorado Experiment Station 
crease with increase of altitude, as from the Missouri river west 
to near the base of the Kocky mountains, then there seems to 
be an increase in the amount to the tops of the higher moun¬ 
tains and on the crest of the range, especially on the wind- 
ward side. There also seem to exist what have been termed 
islands of greater rainfall, where the precipitation, especially 
in winter, seems to he great deal more than on the lower levels. 
In our case the line of lowest rainfall seems to be some 30 or 40 
miles east of the foothills, and to increase to the eastward as 
well as westward to the summit of the mountains. The exist¬ 
ence of islands of greater rainfall has long been noticed, several 
of which are found in this State. The rainfall in some of the 
>^iore favored localities is at least twice as much as it is only a 
short distance away. These islands aften occur at the sources 
of our larger streams, and since it is from the slowly melting 
snow on the high mountains that a fairly constant stream of 
water is available for the irrigation of the valley lands, the 
snowfall is very important to the well being of the people of 
the State, particularly those engaged in agriculture. 
GREATEST RAINFALL IN APRIL, MAY, JUNE AND JULY 
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 10.68 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 rain¬ 
fall of the State as a whole averages about 15 inches annually, 
the rainy season being in the spring and early summer months. 
Idle portion falling in the mountainous 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 
percent but, falling on a comparatively flat surface, the mois¬ 
ture is absorbed by the soil and is directly available to the cul¬ 
tivated crops or natural stock range. An accurate knowledge 
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 region is occasionally visited by long dry 
spells. Since the distribution of pressure which brings about 
this condition is generally wide-spread, the dry periods pre¬ 
vail 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, 
