2 BULLETIN 959, U. S. DEPARTMENT OF AGRICULTURE. 
THE GRAND VALLEY OF COLORADO. 
The Grand Valley is one of the most important fruit-growing 
regions of Colorado, having approximately 15,000 acres devoted to 
such fruits as apples, pears, peaches, plums, cherries, and bush fruits, 
About 10,000 of these acres are planted to apples and 2,500 to pears, 
both of which (and particularly the apple) are heavily attacked by 
the codling moth. 
LOCATION AND TOPOGRAPHY. 
The Grand Valley is in the western part of Mesa County and ex- 
tends from Palisades to Fruita, about 32 miles. The valley follows 
the course of the Grand River and is generally level, except for the 
sections known as the Fruit Ridges, which are somewhat elevated 
and rolling. The district of Orchard Mesa, although higher than the 
rest of the valley, is typical level, or mesa, land. The lower part of 
the valley is approximately 4,500 feet-above sea level and the upper 
district at Palisades is about 4,800 feet in elevation. 
CLIMATE. 
The climate is comparatively dry, and the crops are irrigated 
principally by means of water taken from the Grand River. The 
annual precipitation is but 8 to 9 inches, and during the five months 
from May to September, in which season the apple and codling moth 
are developing, the rainfall amounts to only from 3 to 4inches. The 
mean normal temperature during the same period is about 70.6° F. 
COMPARISON OF THE CLIMATIC CONDITIONS OF GRAND JUNCTION, COLO., AND 
ROCHESTER, N. Y.3 
Since the development and severity of the codling moth are largely 
influenced by climatic factors, it may be of interest to compare the 
weather conditions of the Grand Valley with those of the western 
New York apple belt. Under the semiarid conditions that exist in 
the Grand Valley, the codling moth causes great injury to the fruit 
crop and is very difficult to control, whereas under the relatively 
cooler and more humid conditions of western New York the codling 
moth is much less troublesome. 
In Table 1 will be found data giving a comparison of the mean 
normal temperature and precipitation of Grand Junction, Colo., and 
Rochester, N. Y.* It will be noted therein that the total normal 
precipitation in the Grand Valley during the growing season, or from 
May to September, inclusive, is only about one-fourth as much as in 
western New York and that the mean temperature is about 6° F. 
higher than that of Rochester, N. Y. 
‘Midst of the western New York apple belt. 
# Climatological data, U.S. Weather Bureau. 
