BULLETIN 268, U. S. DEPARTMENT OF AGRICULTURE. 
The Great Plains area to which the conclusions in this bulletin 
apply is shown by the map (fig. 1). The dots show the locations of 
the 14 field stations mentioned. The eastern boundary of the area 
is the ninety-eighth meridian and the western boundary is the 5,000- 
foot contour along the eastern foothills of the Rocky Mountains. 
The altitude along 
the eastern boundary 
ranges from approxi- 
mately 1,000 feet in 
the southeastern por- 
tion to 1,400 in the 
northeastern. The 
average altitude of 
the southern portion 
is higher than that of 
the northern. The 
length of the area 
from north to south 
is about 1,000 miles 
and the width from 
east to west about 
400 miles. The area 
contains, therefore, 
about 400,000 square 
miles. 
The period of time 
covered by the inves- 
tigations at the sev- 
eral stations ranges 
from two to eight 
years. The aggre- 
gate of the years at 
all these stations is 80 . 
The average number 
of the separate plats 
used each year is 
1,900. The number 
of moisture determi- 
nations made at all the stations during the entire period is approxi- 
mately 91,000. 
The work has been conducted in cooperation with the State agri- 
cultural experiment stations in Montana, North Dakota, Nebraska, 
and Kansas, and with the Biophysical Laboratory, the Office of 
Western Irrigation Agriculture, and the Office of Cereal Investiga- 
Fig. 1.— Sketch map of the Great Plains area, which includes parts 
of. ten States and consists of about 400,000 square miles of territory. 
Its western boundary is indicated by the 5,000-foot contour. The 
location of each field station within the area is shown by a dot 
within a circle (0). 
