Native Vegetation 
21 
Rocky Mountains in Colorado he has often noticed that elevated 
stations retain a mild temperature for some time after a cold wave 
has set in at a lower level. Marked temperature inversion has been 
observed in the orchard sections of western Colorado. As pointed 
out on page 8, the mean temperature for January, 1915, at Marble 
(7,951 feet) was 6° higher than at Glenwood Springs (5,758 feet) 
in the same drainage system, and that at Cedaredge (6,175 feet) 
was 3.9° higher than at Delta (5,025 feet). 
Batchelor and West* have shown, in the neighborhood of 
Logan, Utah, that “The minimum temperatures experienced by the 
brush lands, and upper slopes of the tillable area in a mountain 
valley average from 6° to 10° warmer than the valley bottoms, 
due to the drainage of cold air to the low areas during the typical 
clear, calm, frosty nights'*’. 
Temperature inversion is largely eliminated by cloudiness and 
by wind movement. Temperatures are not as low at the mouths 
of canyons where canyon breezes exert an influence, as they are 
at stations of about the same elevation which are not under the 
influence of these breezes. 
PRECIPITATION 
Mean Annual Precipitation .—In making a mean annual pre¬ 
cipitation map of Colorado it is found difficult to depend entirely 
upon rain-gage records, for in some sections of the state stations 
are so very far apart and the topographical conditions between 
them may be so varied as to indicate quite clearly that the rain¬ 
fall and snowfall are much different in amount from that indi¬ 
cated by the nearest stations. Therefore, in the construction of 
the precipitation map (Fig. 8), not only were all available records 
taken into account, but the directions of lines at intermediate 
points were guided by topography, and by the character of the 
native plant associations. 
The portions of Colorado with an average annual precipita¬ 
tion less than 10 inches include most of the San Luis Valley and 
the lower altitudes in the Grand and Uncompaghre drainages. A 
large percentage of Colorado has an annual precipitation between 
10 and 15 inches. This includes the western half of the Great 
' Plains lying next to the foothills, a corner in the southeast, much 
of South Park and the Wet Mountain Valley, most of North 
Park, almost all of the northwest counties, intermediate elevations 
in the western valleys, lower altitudes in Montezuma, Dolores and 
♦Batchelor, L. D., and West, F. L. Variation in minimum temperatures due to the 
topography of a mountain valley in its relation to fruit growing. Utah Agr. Exp. Sta., 
Bui. 141:1-27. 1915. 
