34 THE U. S. GEOLOGICAL SURVEY 



scale selected varying with the character of the area mapped 

 and the degree of detail required. These scales are 1 162,500, 

 1:125,000, and 1:250,000; that is, approximately 1 mile, 2 

 miles, and 4 miles to the inch, respectively. A sheet thus rep- 

 resents an area of approximately 230 square miles, 920 square 

 miles, or 3,700 square miles. The largest scale, showing the 

 most detail and representing the smallest area, is used for 

 densely populated or otherwise important areas ; the next larg- 

 est for sparsely inhabited mountain regions; the smallest for 

 areas covered by reconnaissance or exploratory surveys, es- 

 pecially in the western states and Alaska. 



The boundaries of each quadrangle, as the area mapped on 

 a single sheet is known, are meridians of longitude and par- 

 allels of latitude, the differences in longitude or latitude be- 

 tween the boundaries being in the largest scale maps 15', and 

 in the smaller scales, 30' and 1", respectively. 



The maps show the topographic features of the land, such 

 as mountains, hills, valleys, and gulches; all bodies of water, 

 such as lakes, marshes, streams, and springs; the routes of 

 travel, such as railroads, wagon roads, and trails ; political 

 boundaries; cities, towns, and permanent buildings; and the 

 names of natural and other features. They also indicate ex- 

 actly the location of permanent survey monuments and bench 

 marks whose positions and whose elevations above sea level 

 have been determined by precise methods. The maps of areas 

 covered by public land surveys show all township and section 

 lines as well as the boundaries of all land grants. 



Each of these maps is printed in three colors — black for the 

 cultural features, such as boundary lines, roads, railroads, 

 houses, towns, and cities, and for the names of all things 

 represented ; brown for the relief, or the element of elevation, 

 indicated by contour lines showing the heights of all parts of 

 the area above sea level; and blue for the water — the rivers, 

 lakes, and the sea and its bays and inlets. 



Each sheet is named from some prominent natural or other 

 feature within the quadrangle it represents, such as a lake, 



