A geologic map is a special-purpose map made for the purpose of showing subsurface geological features. In the United States, geologic maps are usually superimposed over a topographic map (and at times over other base maps) with the addition of a color mask with letter symbols to represent the kind of geologic unit, stratigraphic contour lines, fault lines, strike and dip symbols, and various additional symbols as indicated by the map key. A map of the world by Johannes Kepler A map is a simplified depiction of a space, a navigational aid which highlights relations between objects within that space. ... Example of a topographic map with contour lines Topographic maps, also called contour maps, topo maps or topo quads (for quadrangles), are maps that show topography, or land contours, by means of contour lines. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ... Stratigraphy, a branch of geology, is basically the study of rock layers and layering (stratification). ... Old fault exposed by roadcut near Harrisburg, Pennsylvania. ...

The color mask denotes the exposure of the immediate bedrock, even if obscured by soil or other cover. Each area of color denotes a geologic unit or particular rock formation (as more information is gathered new geologic units may be defined). However, in areas where the bedrock is overlain by a significantly thick unconsolidated burden of till, terrace deposits, loess deposits, or other important feature, these are shown instead. Bedrock is the native consolidated rock underlying the Earths surface. ... Sedimentary, volcanic, plutonic, metamorphic rock types of North America. ... Loose, unattached, unstratified particles of earth material such as gravel, sand, sediment or dust, without combined rigidity or cohesiveness due to a lack of binding or natural mineral cement (such as gypsum or limestone) to hold it together; as opposed to consolidated. ... This article is about glacial sediments, for other uses see till (disambiguation). ... A terrace is: In agriculture, a levelled section of a hilly cultivated area, designed to slow or prevent the rapid run-off of irrigation water. ... Loess is a fine, silty, windblown (eolian) type of unconsolidated deposit, or, sometimes the term refers to the soil derived from it. ...

The stratigraphic contour lines are drawn on the surface of a selected deep stratum, so that they can show the topographic trends of the strata under the ground. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Interstate road cut through limestone and shale strata in eastern Tennessee In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. ...

Strike and dip symbols consist of (at minimum) a long line, a number, and a short line which are used to indicate tilted beds. The long line is the strike line, which shows the true horizontal direction along the bed, the number is the dip or number of degrees of tilt above horizontal, and the short line is the dip line, which shows the direction of tilt.

Whereas topographic maps are produced by the United States Geological Survey in conjunction with the states, geologic maps are usually produced by the states. There are almost no geologic map resources for some states, while a few states, such as Kentucky, are extensively mapped geologically. Example of a topographic map with contour lines Topographic maps, also called contour maps, topo maps or topo quads (for quadrangles), are maps that show topography, or land contours, by means of contour lines. ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ... State nickname: Bluegrass State Other U.S. States Capital Frankfort Largest city Louisville Governor Ernie Fletcher Official languages English Area 104,749 km² (37th)  - Land 102,989 km²  - Water 1,760 km² (1. ...

The oldest preserved geologic map is the Turin papyrus, made around 1150 BCE for gold deposits in Egypt. The Turin Papyrus is an ancient Egyptian map, generally considered the oldest surviving map of topographical interest from the ancient world. ... General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ...

See also

• Geology
• Geography
• Cartography

Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ... Cartography or mapmaking (in Greek chartis = map and graphein = write) is the study and practice of making maps or globes. ...

External links

• Geologic Maps from USGS National Park Service
• USGS National Geologic Map Database