BULLETIN 268, U. S. DEPARTMENT OP 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 (©). 



