28 BULLETIN 618, U. S. DEPARTMENT OF AGRICULTURE. 
109° 107° 105° 
|0 ,O C, 3 o 97 C 
107° 105 
103° 101° 
Fig. 10. — Map of the Great Piains area, showing the altitudes above sea level by means of lines follow- 
ing the contours at 1,000, 1,500, 2,000, 3,000, 4,0C0, 5,000, and 6,000 feet. 
