306 



EEPOET UNITED STATES GEOLOGICAL SURVEY. 



peaks, with their heights, &c. Upon this map as a base are printed the 

 general geologic and economic maps of the whole State of Colorado. 



The economic map has been constructed from notes taken by the 

 members of the different parties while in pursuit of their regular duties. 

 Upon this sheet are given as nearly as possible the outlines of the agri- 

 cultural, grazing, timber, mineral, and desert lands, each represented 

 by different colors. 



The atlas also contains two sheets of geological sections, and two of 

 characteristic i)anoramic views. These, with the primary triangulatiou 

 map, completes the atlas. 



DECLTNATION OF THE MAGNETIC NEEDLE. 



I give below a table of declinations of the magnetic needle, with the 

 approximate latitudes and longitudes of the points of observation. It 

 will be seen at a glance that little dependence can be placed on the com- 

 pass over the greater part of this region, especially in the mountain 

 portions, where the variation has a range from 5° to 24°, and this occurs 

 in a small area. 



In the plains and mesa country of the southwestern part of Colorado 

 the declination is much more regular, ranging from 13° to 15°. The 

 declination all along the southern part of Colorado and northern i)ortion 

 of New Mexico is about 13° 30', where it is not disturbed by local at- 

 tractions. This gradually increases as you go north until it reaches 

 15'^ 30' at the northern border of the State. 



It will be seen from the table that it is difficult to give any definite 

 declination for even a small area of country, as the local attraction varies 

 greatly within a small area. 



This wide range of the magnetic variation has no doubt been a very 

 fruitful source of error in all of the older explorations through the interior, 

 when in their meandering systems so much dependence had to be placed 

 on the compass, and, having no fixed points to correct these errors by, 

 they must have accumulated to considerable proportions over every con- 

 siderable area of country or every extended line, even though they were 

 often checked by azimuth observations. 



Point of observation. 



03 

 .-1 



o 



S 



Date. 



1 



n 



Station 1 



o / 



SB 29 

 38 25 

 38 30 

 38 27 

 38 28 

 38 20 

 38 17 

 38 31 

 38 27 

 38 14 

 38 11 



37 54 



38 08 

 38 13 

 38 23 

 38 17 

 38 20 



37 55 



38 01 

 38 10 

 38 24 

 38 29 

 38 41 

 38 49 

 38 42 

 38 35 



o / 

 106 00 

 106 13 

 106 15 

 105 50 

 105 51 

 105 42 

 105 33 

 105 22 

 105 16 

 105 18 

 105 26 

 105 33 

 105 43 

 105 45 



105 50 



106 06 

 106 13 

 106 32 

 106 55 

 306 02 

 106 42 

 106 31 

 106 37 

 106 39 

 106 27 

 106 22 



1873. . 



July 



do 



....do 



-.-.do 



....do 



....do 



....do 



....do 



....do 



....do 



do 



....do 



....do 



....do 



....do 



....do 



August 



....do 



....do 



....do 



....do 



....do 



....do 



....do 



....do 



....do 



o / 



14 40 





12 26 





12 10 





14 30 





11 00 





16 40 





16 ?3 





14 30 





9 30 





22 40 





15 35 





15 27 



Station 19 



15 01 



Mount Kito Alto. • . 



15 38 





14 10 



Station 23 



12 06 



Station 24 



19 47 



Station 28 T 



13 25 



Station 33 



17 40 





14 23 





15 10 



Station 37 .,,. 



Station 38 



13 30 



14 40 





14 40 





15 50 



Station 45 



14 00 



