REPORT ON THE ARABLE AND PASTURE LANDS OF COLORADO. 



By Henry Gannett, M. E 



CHAPTER! 

 PHYSICAL GEOGRAPHY. 



TOPOGRAPHY. 



The area of Colorado is 104,500 square miles. Of this, nearly all of the 

 eastern half, or about 45,500 square miles, consists of plains; the middle 

 portion, comprising about 32,000 square miles, is mountain country, more 

 or less rugged, containing several large valleys, most of which are at a 

 considerable elevation ; while the western portion, or 17,000 square miles, 

 consists of plateau country. 



The mean height of the State above the sea is 7,000 feet, being the 

 highest of the States or Territories. The lowest part of the State is at 

 its eastern boundary, where it is little above 3,000 feet, while the high- 

 est mountain-summits reach altitudes above 14,000 feet. 



The areas between the different thousand-foot contour-lines are given 

 in the following table: 



Square miles. 



Between 3,000 and 4,000 feet 9,000 



Between 4,000 and 5,000 feet 21,800 



Between 5,000 and 6,000 feet 15,000 



Between 6,000 and 7,000 feet 10,000 



Between 7,000 and 8,000 feet 11,000 



Between 8,000 and 9,000 feet 14,000 



Between 9,000 aod 10,000 feet 10,000 



Between 10,000 and 11,000 feet 6,800 



Between 11,000 anil 12,000 feet... 5,000 



Between 12,000 and 13,000 feet 1,400 



Above 13,000 feet 500 



The general slope of the plains is toward the eastward. At the base 

 of the mountains they are from 5,000 to 7,500 feet above the sea, while at 

 the eastern boundary of the State the elevation is 3,000 to 4,000 feet. 

 Their surface is rolling or undulating, with broad, flat valleys and low 

 divides. 



The plains are drained by the South Platte, Republican, and Arkan- 

 sas Rivers with their branches. The first and last have their sources in 

 the mountains in many streams, which unite in the plains. The other 

 stream rises and has its course entirely in the plains. 



From the foot of the mountains, in latitude 39°, an elevated swell in 

 the plains in the form of a flat, broad ridge, runs eastward, separating 

 the drainage of the Arkansas from that of the South Platte. This, 

 known as "The Divide," or "The Arkansas Divide," is about 7,500 feet 

 in elevation, but decreases in height eastward. Northward, the plains at 

 the foot of the mountains slope gently down to a mean elevatiou of be- 

 tween 5,000 and 6,000 feet. Southward the slope is more rapid, reach- 

 ing a height of 5,000 feet at the debouchure of the Arkansas from the 

 mountains; thence the general level rises again, and keeps a mean ele- 

 vation not far from 5,500 feet to the southern boundary of the State. 



With the exception of a few groups of eruptive mountains, the whole 

 mountain area is made up of a succession of parallel ranges and valleys, 



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