Geologic map

A geologic map or geological map is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface. Bedding planes and structural features such as faults, folds, foliations, and lineations are shown with strike and dip or trend and plunge symbols which give these features' three-dimensional orientations.

Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. 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.

Geological map Britain William Smith 1815
William Smith's geologic map
World geologic provinces
Mapped global geologic provinces



Rock units are typically represented by colors. Instead of (or in addition to) colors, certain symbols can be used. Different geologic mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of differing types and ages.


A standard Brunton Geological compass, used commonly by geologists

Geologists take two major types of orientation measurements (using a hand compass like a Brunton compass): orientations of planes and orientations of lines. Orientations of planes are often measured as a "strike" and "dip", while orientations of lines are often measured as a "trend" and "plunge".

Strike and dip symbols consist of a long "strike" line, which is perpendicular to the direction of greatest slope along the surface of the bed, and a shorter "dip" line on side of the strike line where the bed is going downwards. The angle that the bed makes with the horizontal, along the dip direction, is written next to the dip line. In the azimuthal system, strike and dip are often given as "strike/dip" (for example: 270/15, for a strike of west and a dip of 15 degrees below the horizontal).

Trend and plunge are used for linear features, and their symbol is a single arrow on the map. The arrow is oriented in the downgoing direction of the linear feature (the "trend") and at the end of the arrow, the number of degrees that the feature lies below the horizontal (the "plunge") is noted. Trend and plunge are often notated as PLUNGE → TREND (for example: 34 → 86 indicates a feature that is angled at 34 degrees below the horizontal at an angle that is just East of true South).


The oldest preserved geologic map is the Turin papyrus (1150 BCE), which shows the location of building stone and gold deposits in Egypt.[1][2]

The earliest geologic map of the modern era is the 1771 "Map of Part of Auvergne, or figures of, The Current of Lava in which Prisms, Balls, Etc. are Made from Basalt. To be used with Mr. Demarest's theories of this hard basalt. Engraved by Messr. Pasumot and Daily, Geological Engineers of the King." This map is based on Nicolas Desmarest's 1768 detailed study of the geology and eruptive history of the Auvergne volcanoes and a comparison with the columns of the Giant's Causeway of Ireland. He identified both landmarks as features of extinct volcanoes. The 1798 report was incorporated in the 1771 (French) Royal Academy of Science compendium.

The first geological map of the U.S. was produced in 1809 by William Maclure.[3] In 1807, Maclure undertook the self-imposed task of making a geological survey of the United States. He traversed and mapped nearly every state in the Union. During the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times.[4][5] Maclure's map shows the distribution of five classes of rock in what are now only the eastern states of the present-day US.

The first geologic map of Great Britain was created by William Smith in 1815 using principles (Smith's laws) first formulated by Smith.[6]

Maps and mapping around the globe

North america terrain 2003 map
Geologic map of North America superimposed on a shaded relief map

United States

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. 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 sediments, loess deposits, or other important feature, these are shown instead. Stratigraphic contour lines, fault lines, strike and dip symbols, are represented with various symbols as indicated by the map key. Whereas topographic maps are produced by the United States Geological Survey in conjunction with the states, geologic maps are usually produced by the individual states. There are almost no geologic map resources for some states, while a few states, such as Kentucky and Georgia, are extensively mapped geologically.

United Kingdom

In the United Kingdom the term geological map is used. The UK and Isle of Man have been extensively mapped by the British Geological Survey (BGS) since 1835; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947.

Two 1:625,000 scale maps cover the basic geology for the UK. More detailed sheets are available at scales of 1:250,000, 1:50,000 and 1:10,000. The 1:625,000 and 1:250,000 scales show both onshore and offshore geology (the 1:250,000 series covers the entire UK continental shelf), whilst other scales generally cover exposures on land only.

Sheets of all scales (though not for all areas) fall into two categories:

  1. Superficial deposit maps (previously known as solid and drift maps) show both bedrock and the deposits on top of it.
  2. Bedrock maps (previously known as solid maps) show the underlying rock, without superficial deposits.

The maps are superimposed over a topographic map base produced by Ordnance Survey (OS), and use symbols to represent fault lines, strike and dip or geological units, boreholes etc. Colors are used to represent different geological units. Explanatory booklets (memoirs) are produced for many sheets at the 1:50,000 scale.

Small scale thematic maps (1:1,000,000 to 1:100,000) are also produced covering geochemistry, gravity anomaly, magnetic anomaly, groundwater, etc.

Although BGS maps show the British national grid reference system and employ an OS base map, sheet boundaries are not based on the grid. The 1:50,000 sheets originate from earlier 'one inch to the mile' (1:63,360) coverage utilising the pre-grid Ordnance Survey One Inch Third Edition as the base map. Current sheets are a mixture of modern field mapping at 1:10,000 redrawn at the 1:50,000 scale and older 1:63,360 maps reproduced on a modern base map at 1:50,000. In both cases the original OS Third Edition sheet margins and numbers are retained. The 1:250,000 sheets are defined using lines of latitude and longitude, each extending 1° north-south and 2° east-west.


The first geological map of Singapore was produced in 1974, produced by the then Public Work Department. The publication includes a locality map, 8 map sheets detailing the topography and geological units, and a sheet containing cross sections of the island.

Since 1974, for 30 years, there were many findings reported in various technical conferences on new found geology islandwide, but no new publication was produced. In 2006, Defence Science & Technology Agency, with their developments in underground space promptly started a re-publication of the Geology of Singapore, second edition. The new edition that was published in 2009, contains a 1:75,000 geology map of the island, 6 maps (1:25,000) containing topography, street directory and geology, a sheet of cross section and a locality map.

The difference found between the 1976 Geology of Singapore report include numerous formations found in literature between 1976 and 2009. These include the Fort Canning Boulder Beds and stretches of limestone.

See also


  1. ^ Harrell, James A.; Brown, V. Max (1992). "The world's oldest surviving geological map—the 1150 BC Turin papyrus from Egypt". The Journal of Geology. 100 (1): 3–18. JSTOR 30082315.
  2. ^ Klemm, Rosemarie; Klemm, Dietrich (2013). Gold and Gold Mining in Ancient Egypt and Nubia. Heidelberg: Springer. pp. 132–136. ISBN 9783642225079.
  3. ^ "Maclure's geological map of the United States". US Library of Congress' Map Collection. Library of Congress. Retrieved 30 October 2015.
  4. ^ Wikisource Chisholm, Hugh, ed. (1911). "Maclure, William" . Encyclopædia Britannica. 17 (11th ed.). Cambridge University Press. p. 263.
  5. ^ Greene, J.C.; Burke, J.G. (1978). "The Science of Minerals in the Age of Jefferson". Transactions of the American Philosophical Society. New. 68 (4): 39. (article pages: 1–113)
  6. ^ Simon Winchester, 2002, The Map that Changed the World, Harper-Collins ISBN 0-06-093180-9

External links

Anseris Mons

Anseris Mons is an isolated massif (mountain) in the southern highlands of Mars, located at the northeastern edge of Hellas Planitia at longitude 86.65°E and latitude 29.81°S. The mountain is 58 km (36 mi) in diameter and rises to an elevation of approximately 4,200 m (13,780 ft) above datum (martian "sea" level) or about 6,200 m (20,300 ft) above the surrounding plains. The mountain lies in the southeastern quarter of the Iapygia quadrangle (MC-21), straddling the boundary with the adjoining Hellas quadrangle (MC-28) to the south.

Anseris Mons is named from Anseris Fons, a telescopic albedo feature mapped by Greek astronomer E. M. Antoniadi in 1930. The name was approved by the International Astronomical Union (IAU) in 1991.Anseris Mons is not a volcano. Geologically, the massif is thought to be the eroded remnant of an ancient crustal block uplifted from depths of several kilometers in the formation of the Hellas impact basin during the period of heavy bombardment. Anseris Mons is the type area for a large set of rugged mountain blocks (>25 km across) that occur in a relatively continuous band 200 to 500 km wide around the western, northeastern, eastern, and southeastern rim of the Hellas basin. Many of the blocks, particularly along the western rim, are concentric with the basin and bounded by faults.Rocks making up Anseris Mons and other massifs around Hellas are mapped as Noachian in age. However, work by Herbert Frey at NASA’s Goddard Spaceflight Center using Mars Orbital Laser Altimeter (MOLA) data indicates that the southern highlands of Mars contain numerous buried impact basins that are older than the visible Noachian-aged surfaces and which pre-date the Hellas impact. He suggests that the Hellas impact should mark the beginning of the Noachian period (base of the Noachian system). If Frey is correct, then Anseris Mons bedrock is actually pre-Noachian in age, perhaps dating back to over 4.1 billion years ago.The Anseris Mons massif has undergone a significant amount of erosion since it was uplifted. The flanks of the mountain have huge triangular re-entrants and associated spurs, which give the massif a broad, pyramidal shape. The re-entrants were likely produced through a variety of mass-wasting and periglacial/glacial processes. A large cirque-like re-entrant with channelized debris aprons or fans is present on the south side of the mountain.


In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core. A typical anticline is convex up in which the hinge or crest is the location where the curvature is greatest, and the limbs are the sides of the fold that dip away from the hinge. Anticlines can be recognized and differentiated from antiforms by a sequence of rock layers that become progressively older toward the center of the fold. Therefore, if age relationships between various rock strata are unknown, the term antiform should be used.

The progressing age of the rock strata towards the core and uplifted center, are the trademark indications for evidence of anticlines on a geologic map. These formations occur because anticlinal ridges typically develop above thrust faults during crustal deformations. The uplifted core of the fold causes compression of strata that preferentially erodes to a deeper stratigraphic level relative to the topographically lower flanks. Motion along the fault including both shortening and extension of tectonic plates, usually also deforms strata near the fault. This can result in an asymmetrical or overturned fold.


In geology, bedrock is the lithified rock that lies under a loose softer material called regolith at the surface of the Earth or other terrestrial planets. The broken and weathered regolith includes soil and subsoil. The surface of the bedrock beneath the soil cover is known as rockhead in engineering geology, and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits (also known as drift) can be extremely thick, such that the bedrock lies hundreds of meters below the surface.Bedrock may also experience subsurface weathering at its upper boundary, forming saprolite.

A solid geologic map of an area will usually show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed.

Beethoven quadrangle

The Beethoven quadrangle is located in the equatorial region of Mercury, in the center of the area imaged by Mariner 10. Most pictures of the quadrangle were obtained at high sun angles as the Mariner 10 spacecraft receded from the planet. Geologic map units are described and classified on the basis of morphology, texture, and albedo, and they are assigned relative ages based on stratigraphic relations and on visual comparisons of the density of superposed craters. Crater ages are established by relative freshness of appearance, as indicated by topographic sharpness of their rim crests and degree of preservation of interior and exterior features such as crater floors, walls, and ejecta aprons. Generally, topography appears highly subdued because of the sun angle, and boundaries between map units are not clearly defined.

Impact craters larger than about 250 km are referred to as basins. Unlike many basins on the Moon, however, the two obvious basins in the quadrangle, Beethoven (610 km in diameter) and Raphael (320 km in diameter), are not multiringed, whereas well-developed rings encircle many craters of lesser diameters. Remnant ejecta blankets around parts of the Beethoven and Raphael basins are subdued in appearance and their margins poorly defined in places. However, where they can be recognized, these extensive aprons allow a generalized regional stratigraphic sequence to be determined. A third basin, extremely subdued but probable, is centered at latitude 0°, longitude 130°.

Mariner 10 images in the northeastern part of the quadrangle are very poor to unusable. This area therefore contains blank patches or only a few crater outlines and mapped materials. Another difficulty in mapping is the poor match in topographic bases between Beethoven and adjacent quadrangles. Mismatches are especially common along the borders with the Kuiper and Discovery quadrangles to the east and southeast.

California Geological Survey

The California Geological Survey, previously known as the California Division of Mines and Geology, is the California state geologic agency.

Data model (GIS)

A data model in geographic information systems is a mathematical construct for representing geographic objects or surfaces as data. For example, the vector data model represents geography as collections of points, lines, and polygons; the raster data model represent geography as cell matrices that store numeric values; and the TIN data model represents geography as sets of contiguous, nonoverlapping triangles.

Denning (Martian crater)

Denning Crater is a large Noachian-age impact crater in the southwestern Terra Sabaea region of the southern Martian highlands, within the Sinus Sabaeus quadrangle. It is located to the northwest of the Hellas impact basin within the furthest outskirts of the Hellas debris apron. The crater is 165 km in diameter and likely formed during the Late Heavy Bombardment, a period of intense bolide impacts affecting the entirety of the Solar System; during the Hesperian period, aeolian processes caused significant degradation of the crater's rim features and infilled the crater's floor (which is nearly at the same elevation as the surrounding plains terrain). Similar to other large craters in this region of Mars, wind-eroded features are sporadically found on the basin floor. The presence of wrinkle ridges of varying orientations within and around the Denning basin has been correlated to regional tectonic events, including the formation of the Hellas basin itself. The crater was named for British astronomer William Frederick Denning.

Donald Wilhelms

Don Edward Wilhelms (born July 5, 1930) is a former United States Geological Survey geologist who contributed to geologic mapping of the Earth's moon and to the geologic training of the Apollo astronauts. He is the author of To a Rocky Moon: A Geologist's History of Lunar Exploration (1993), The geologic history of the Moon (1987), and he co-authored the Geologic Map of the Near Side of the Moon (1971) with John F. McCauley. Wilhelms also contributed to Apollo Over the Moon: A View from Orbit (NASA SP-362). He has also contributed to the study of Mars (including Mariner 9), Mercury, and Ganymede.

Geologic map of Georgia (U.S. state)

The geologic map of Georgia (a state within the United States) is a special-purpose map made to show geological features. Rock units or geologic strata are shown by colors or symbols to indicate where they are exposed at the surface. Structural features such as faults and shear zones are also shown. Since the first national geological map, in 1809, there have been numerous maps which included the geology of Georgia. The first Georgia specific geologic map was created in 1825. The most recent state-produced geologic map of Georgia, by the Georgia Department of Natural Resources is 1:500,000 scale, and was created in 1976 by the department's Georgia Geological Survey. It was generated from a base map produced by the United States Geological Survey. The state geologist and Director of the Geological Survey of Georgia was Sam M. Pickering, Jr. Since 1976, several geological maps of Georgia, featuring the state's five distinct geologic regions, have been produced by the federal government.

Geology of Georgia (U.S. state)

The Geology of Georgia consists of four distinct geologic regions, beginning in the northwest corner of the state and moving through the state to the southeast: the Valley and Ridge region, also known as the Appalachian Plateau; the Blue Ridge; the Piedmont and the Coastal Plain. The Fall Line is the boundary between the Piedmont and the Coastal Plain.

Hamilton Group

The Devonian Hamilton Group is a mapped bedrock unit in the United States. The unit is present in New York, Pennsylvania, Maryland, Ohio and West Virginia. In Virginia, it is known as the laterally equivalent Millboro Shale.

The group is named for the village of Hamilton, New York.

Details of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line from the National Geologic Map Database.

These rocks are the oldest strata of the Devonian gas shale sequence.

Kuiper quadrangle

The Kuiper quadrangle, located in a heavily cratered region of Mercury, includes the young, 55-km-diameter crater Kuiper (11° S., 31.5° ), which has the highest albedo recorded on the planet, and the small crater Hun Kal (0.6° S., 20.0° ), which is the principal reference point for Mercurian longitude (Davies and Batson, 1975). Impact craters and basins, their numerous secondary craters, and heavily to lightly cratered plains are the characteristic landforms of the region. At least six multiringed basins ranging from 150 km to 440 km in diameter are present. Inasmuch as multiringed basins occur widely on that part of Mercury photographed by Mariner 10, as well as on the Moon and Mars, they offer a potentially valuable basis for comparison between these planetary bodies.

Mahantango Formation

The Devonian Mahantango Formation is a mapped bedrock unit in Pennsylvania, West Virginia, and Maryland. It is named for the North branch of the Mahantango Creek in Perry and Juniata counties in Pennsylvania. It is a member of the Hamilton Group, along with the underlying the Marcellus Formation Shale. South of Tuscarora Mountain in south central Pennsylvania, the lower members of this unit were also mapped as the Montebello Formation.

Details of the type section and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database.

Puget Sound faults

The Puget Sound faults under the heavily populated Puget Sound region (Puget Lowland) of Washington state form a regional complex of interrelated seismogenic (earthquake-causing) geologic faults. These include (from north to south, see map) the:

Devils Mountain Fault

Strawberry Point and Utsalady Point faults

Southern Whidbey Island Fault (SWIF)

Rogers Belt (Mount Vernon Fault/Granite Falls Fault Zone)

Cherry Creek Fault Zone

Rattlesnake Mountain Fault Zone

Seattle Fault

Tacoma Fault

Saddle Mountain Faults

Olympia structure (suspected fault)

Doty Fault

Saint Helens Zone and Western Rainier Zone

Strike and dip

Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike (or strike angle) can be given as either a quadrant compass bearing of the strike line (N25°E for example) or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025), or the azimuth number followed by the degree sign (example of N25°E would be 025°).

The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane, and is given by the number (0°-90°) as well as a letter (N,S,E,W) with rough direction in which the bed is dipping downwards. One technique is to always take the strike so the dip is 90° to the right of the strike, in which case the redundant letter following the dip angle is omitted (right hand rule, or RHR). The map symbol is a short line attached and at right angles to the strike symbol pointing in the direction which the planar surface is dipping down. The angle of dip is generally included on a geologic map without the degree sign. Beds that are dipping vertically are shown with the dip symbol on both sides of the strike, and beds that are level are shown like the vertical beds, but with a circle around them. Both vertical and level beds do not have a number written with them.

Another way of representing strike and dip is by dip and dip direction. The dip direction is the azimuth of the direction the dip as projected to the horizontal (like the trend of a linear feature in trend and plunge measurements), which is 90° off the strike angle. For example, a bed dipping 30° to the South, would have an East-West strike (and would be written 090°/30° S using strike and dip), but would be written as 30/180 using the dip and dip direction method.

Strike and dip are determined in the field with a compass and clinometer or a combination of the two, such as a Brunton compass named after D.W. Brunton, a Colorado miner. Compass-clinometers which measure dip and dip direction in a single operation (as pictured) are often called "stratum" or "Klar" compasses after a German professor. Smartphone apps are also now available, that make use of the internal accelerometer to provide orientation measurements. Combined with the GPS functionality of such devices, this allows readings to be recorded and later downloaded onto a map.Any planar feature can be described by strike and dip. This includes sedimentary bedding, faults and fractures, cuestas, igneous dikes and sills, metamorphic foliation and any other planar feature in the Earth. Linear features are measured with very similar methods, where "plunge" is the dip angle and "trend" is analogous to the dip direction value.

Apparent dip is the name of any dip measured in a vertical plane that is not perpendicular to the strike line. True dip can be calculated from apparent dip using trigonometry if the strike is known. Geologic cross sections use apparent dip when they are drawn at some angle not perpendicular to strike.

Structural basin

A structural basin is a large-scale structural formation of rock strata formed by tectonic warping of previously flat-lying strata. Structural basins are geological depressions, and are the inverse of domes. Some elongated structural basins are also known as synclines. Structural basins may also be sedimentary basins, which are aggregations of sediment that filled up a depression or accumulated in an area; however, many structural basins were formed by tectonic events long after the sedimentary layers were deposited.

Basins may appear on a geologic map as roughly circular or elliptical, with concentric layers. Because the strata dip toward the center, the exposed strata in a basin are progressively younger from the outside in, with the youngest rocks in the center. Basins are often large in areal extent, often hundreds of kilometers across.

Structural basins are often important sources of coal, petroleum, and groundwater.

Tooting (crater)

Tooting is a multi-layered Volcanic Crater (a type of rampart crater) at 23.1°N, 207.1°E, in Amazonis Planitia (Amazonis quadrangle), due west of the volcano Olympus Mons, on Mars. . It was identified by planetary geologist Peter Mouginis-Mark in September 2004. Scientists estimate that its age is on the order of hundreds of thousands of years, which is relatively young for a Martian crater. A later study confirms this order of magnitude estimate. A preliminary paper describing the geology and geometry of Tooting was published in 2007 by the journal "Meteoritics and Planetary Science", vol. 42, pages 1615 - 1625. Further papers have more recently been published, including a 2010 analysis of flows on the walls of Tooting crater by A.R. Morris et al. ("Icarus vol. 209, p. 369 - 389), and a 2012 review paper by P.J. Mouginis-Mark and J.M. Boyce in "Chemie der Erde Geochemistry", vol. 72, p. 1 - 23. A geologic map has also been submitted in 2012 to the U.S. Geological Survey for consideration and future publication.


The Uzboi-Landon-Morava (ULM) outflow system is a long series of channels and depressions that may have carried water across a major part of Mars. It starts with channels that drain into the Argyre basin in the Argyre quadrangle. Water ponded in the Argyre basin, then the overflow is believed to have traveled northward through Uzboi Vallis, into Landon basin, through Morava Valles, to the floor of Margaritfier basin. Some of the water may have helped to carve Ares Vallis. Altogether, the total area drained for this watershed may have been about 11 X 106 km2 or about 9% of Mars.Pictures below show the Argyre basin which was once full of water. Also, the wider view shows the distance the water traveled, which was south of Argyre basin to Margaritifer Terra.


Zincography was a planographic printing process that used zinc plates. Alois Senefelder first mentioned zinc's lithographic use as a substitute for Bavarian limestone in his 1801 English patent specifications. In 1834, Federico Lacelli patented a zincographic printing process, producing large maps called géoramas. In 1837–1842, Eugène-Florent Kaeppelin perfected the process to create a large polychrome geologic map.

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