2014

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration

Geologic Map of Mars

By Kenneth L. Tanaka, James A. Skinner, Jr., James M. Dohm, Rossman P. Irwin, III, Eric J. Kolb, 

Corey M. Fortezzo, Thomas Platz, Gregory G. Michael, and Trent M. Hare

Pamphlet to accompany

Scientific Investigations Map 3292

View of the northern part of the western hemisphere of Mars. Left half shows a color elevation, shaded relief view 

highlighting the immense shields of the Tharsis rise. Right half shows a true-color view of the vast Valles Marineris and 

Kasei Valles canyon systems, which connect to the dark basin of Chryse Planitia at upper right. (Image data from NASA.)

i

Contents

Introduction ....................................................................................................................................................1

Physiographic Setting...................................................................................................................................2

Data .................................................................................................................................................................3

Mapping Methods..........................................................................................................................................3

Map Development and Author Roles .........................................................................................................4

Unit Delineation.....................................................................................................................................4

Unit Groups ............................................................................................................................................5

Unit Names and Labels........................................................................................................................5

Contact Types ........................................................................................................................................5

Line Feature Types................................................................................................................................6

Drafting ..................................................................................................................................................6

Age Determinations.......................................................................................................................................6

Geologic History.............................................................................................................................................9

Noachian Period ...................................................................................................................................9

Early Noachian Epoch........................................................................................................................10

Middle Noachian Epoch ...................................................................................................................10

Late Noachian Epoch ........................................................................................................................11

Hesperian Period ................................................................................................................................12

Early Hesperian Epoch..............................................................................................................12

Late Hesperian Epoch...............................................................................................................13

Amazonian Period...............................................................................................................................13

Early Amazonian Epoch ...........................................................................................................14

Middle Amazonian Epoch ........................................................................................................14

Late Amazonian Epoch .............................................................................................................15

Major Results................................................................................................................................................15

Acknowledgments.......................................................................................................................................15

References Cited..........................................................................................................................................16

Tables

1. Martian epoch lower boundary ages..................................................................................................25 

2. Assigned model ages for selected Mars global map units..........................................................26

3. Total crater densities for map units on Mars ................................................................................32

4. Impact craters and basins (and possible impact-like features of other origin) on Mars .........34

5. Basis for time-stratigraphic assignments for each map unit as shown in the

 Correlation of Map Units................................................................................................................. 37

6. Percentages of previously mapped Viking-based map units for each unit in

 this Mars global map ..................................................................................................................39

7. Percentages of map units in this Mars global map for each previously 

 mapped Viking-based map unit .................................................................................................41
ii
1

Introduction

Mars is the fourth planet from the Sun and the outermost of 

the rocky, terrestrial planets that make up the inner solar system. 

Of this planetary family, Mars is only larger than Mercury. 

Surface gravity on Mars is 3.71 m/s2, which is 37.6 percent that 

of the Earth’s. The present atmospheric pressure is low (~0.6 

kPa) relative to Earth’s (101 kPa), and the atmosphere is mostly 

carbon dioxide (95%). The obliquity of Mars is presently 25° 

and may have varied by tens of degrees over the past tens of 

millions of years and longer (Laskar and others, 2004). 

The Martian polar ice caps, observable from Earth, are 

made up mostly of water ice. Thus the possibilities of liquid 

water and habitable environments on or near the surface of Mars 

have driven interest in the planet (for example, Des Marais, 

2010). Orbiting at a distance on average about 50 percent farther from the Sun than the Earth, Mars is the only other planet 

besides the Earth that is within the solar system’s potential 

habitable zone (Kopparapu and others, 2013). 

Beginning in the late 1960s with the Mariner 4, 6, and 

7 fly-bys, spacecraft began imaging the planet from closer 

perspectives (Snyder and Moroz, 1992). Mariner 9 (1971–72) 

was the planet’s first orbiter, and it successfully imaged the 

entire globe at 2 to 3 km/pixel resolution. These early spacecraft 

revealed the planet’s Moon-like cratered highlands, immense 

volcanoes, huge tectonic rifts, and, strikingly, evidence for 

flowing water in the planet’s ancient past, based on identification of branching valley network systems and broad outflow 

channels. The next major phase of spacecraft exploration in the 

late 1970s and early 1980s involved the two Viking Orbiters and 

two Viking Landers. The orbiters imaged the surface at tenfold 

to hundredfold increased detail, and the landers performed the 

first biological experiments in search of Martian life (*, Klein 

and others, 19921

). The most recent phase of Mars exploration, 

since the late 1990s, has led to significant increase in the types, 

spatial resolution, and amount of data returned both from Mars 

orbit and the surface (*, Barlow, 2008; Bell, 2008). Post-Viking 

orbiters include Mars Global Surveyor, Mars Odyssey, Mars 

Express, and Mars Reconnaissance Orbiter. These have delivered high-resolution visible, thermal, and multispectral imaging; 

laser altimetry; radar, gravity, and magnetic sounding; and other 

measurements of the Martian surface, atmosphere, and crust. 

Rovers and stationary landers, including Mars Pathfinder, Spirit 

and Opportunity Mars Exploration Rovers, Mars Phoenix, and 

the Curiosity Mars Science Laboratory, have performed increasingly sophisticated surface investigations.

Each major phase of exploration has resulted in a global 

geologic map, which encapsulates the most significant advances 

in understanding of Martian surface evolution. The first global 

map of Mars was produced by Scott and Carr (1978) at a scale 

of 1:25,000,000 using Mariner 9 visible wavelength images 

(2–3 km/pixel resolution). That map included compilation of a 

partly completed, 30-quadrangle, 1:5,000,000-scale geologic 

map series drafted by various authors. Scott and Carr (1978) 

identified 24 global geologic units among 5 terrain groups 

and established the 3 principal time-stratigraphic divisions 

for Mars—the Noachian, Hesperian, and Amazonian Periods 

(from oldest to youngest). The second global map of Mars was 

published in three parts at a scale of 1:15,000,000. Western and 

eastern equatorial regions (lat <57°) were produced by Scott 

and Tanaka (1986) and Greeley and Guest (1987), respectively. 

Polar regions (lat >55°) were produced by Tanaka and Scott 

(1987). Viking Orbiter images mostly between 100 and 300 

m/pixel resolution served as the bases for these maps, which 

identified 90 map units, including units of local to global extent. 

Some of these units were used as referents to subdivide the 

time-stratigraphic periods of Scott and Carr (1978) into epochs 

(Early, Middle, and Late Noachian; Early and Late Hesperian; 

and Early, Middle, and Late Amazonian), as well as to establish 

the crater-density values for their boundaries (Tanaka, 1986). 

Both the Mariner 9- and Viking-based geologic maps were originally drafted over shaded-relief-map bases that were manually 

airbrushed using reference images (Batson and others, 1979).

Herein, we present a new global geologic map of Mars, 

which records the distribution of geologic units and landforms 

on the planet’s surface through time, based on unprecedented 

variety, quality, and quantity of remotely sensed data acquired 

since the Viking Orbiters. These data have provided morphologic, topographic, spectral, thermophysical, radar sounding, 

and other observations for integration, analysis, and interpretation in support of geologic mapping. In particular, the precise 

topographic mapping now available has enabled consistent 

morphologic portrayal of the surface for global mapping; 

whereas previously used visual-range image bases were less 

effective, because they combined morphologic and albedo information and, locally, atmospheric haze. Also, thermal infrared 

image bases used for the new map tended to be less affected by 

atmospheric haze, making them reliable for analysis of surface 

morphology and texture at even higher resolution than the 

topographic products. Moreover, following publication of the 

Viking-based global map of Mars, a multitude of geologic maps 

of different parts of the Martian surface at various scales using 

the Viking Orbiter and subsequent datasets were produced to 

address important questions regarding Martian surface geology and evolution; major results from these efforts, mostly at 

1:1,000,000 and smaller (zoomed-out) scales, have been incorporated herein (the locations of these maps are shown in fig. 2). 

Finally, a host of other published studies have contributed to the 

interpretations and geologic reconstruction contained herein. To 

keep our reference list at a reasonable length, we precede some 

citation lists with an asterisk (*, see footnote 1) to indicate that 

other useful, particularly earlier, publications exist.

We used digital photogeologic mapping techniques to 

identify and discriminate 44 geologic units (encompassing ~1,300 separate occurrences) and 12 linear feature types 

(>3,500 individual features mapped, not all shown on map, 

included in digital files), which collectively document major 

episodes of unit emplacement and modification. Along with 

cross-cutting relations, analysis of global as well as specific 

detailed impact crater size-frequency distributions provide an 

unprecedented documentation of relative and modeled absolute 

1

An asterisk (*) is included where only a small sample, generally recent, of 

the many representative publications are cited.
2

ages of map units and their individual occurrences (see tables 

1–3 and D12 at http://pubs.usgs.gov/sim/3292/ and fig. 1), 

as well as chronostratigraphic ages for all impact craters and 

basins >150 km in diameter (table 4). Key stratigraphic relations and crater-density data are used to constrain the timestratigraphic age assignments for each map unit as shown in 

the Correlation of Map Units; this information is summarized 

in table 5. Due to our focus on global (vs. regional) reconstructions, we avoid dividing units based upon modest regional 

variations in age and physical character. These efforts result in 

an improved characterization of Mars compared to the previous, 

Viking-based mapping (tables 6 and 7) and, therefore, provide a 

refined portrayal of Mars’ geologic character and evolution.

Physiographic Setting

The global topography of Mars defines broad regions of 

geologic significance that include geographic names established 

by the International Astronomical Union (IAU). We include 

only names of major features and a representative selection 

of others mentioned herein; see the topographic map of Mars 

(U.S. Geological Survey, 2003) and the Gazetteer of Planetary 

Nomenclature (http://planetarynames.wr.usgs.gov/) for more 

detailed information about and portrayals of Martian geographic 

features. 

Densely cratered, rugged highlands cover much of the 

southern latitudes and some parts of the northern hemisphere of 

Mars, including Arabia Terra, Terra Sabaea, and Tempe Terra. 

Most highlands are between 0 to 5,000 m above datum, which 

is defined at Mars’ mean planetary radius (Smith and others, 

1999, 2001). However, Arabia Terra and parts of other highland 

areas north of the equator lie at 0 to –3,000 m elevations. The 

northern plains lie even lower in elevation, mostly in the range 

of –4,000 to –5,000 m. They are much less cratered than the 

highlands, indicating that burial by younger rock and sediment 

sequences has obscured much of the earlier geologic record. 

The three largest, well-preserved impact basins in the Martian 

cratered highlands are Hellas basin (~2,400 km in diameter and 

includes the deepest surface point on the planet at –8,200 m 

elevation), Isidis basin (~1,500 km in diameter) along the highland-lowland margin, and Argyre basin (~900 km in diameter). 

Utopia Planitia forms the floor of a giant (nearly 3,000 km in 

diameter) circular basin northeast of Isidis Planitia, interpreted 

by many to be an ancient impact basin (*, McGill, 1989). Other 

circular but generally less well defined broad depressions that 

also may be impact structures occur across Mars (*, Schultz and 

others, 1982; Frey, 2006).

The zone of transition between the Martian highlands 

to the south and the lowlands to the north (mostly –1,000 to 

–4,000 m) is marked by diverse landforms, including scarps, 

knobs, mesas, and plateaus that are hundreds of meters to a few 

kilometers in relief. These landforms extend from the southern 

margins of Acidalia Planitia eastward to the southern margin of 

Amazonis Planitia. A gigantic system of linear canyons, Valles 

Marineris, forms along the northern margin of the Thaumasia 

plateau and extends for >2,000 km from Noctis Labyrinthus 

along the eastern margin of the Tharsis rise. The canyon system 

connects to the east with chaotic fields of knobs and mesas 

that mark the source regions of the broad outflow channels of 

circum-Chryse; the channels dissect highland surfaces to depths 

of several kilometers over areass that extend a few thousand 

kilometers prior to their entrance into Chryse Planitia (*, Rotto 

and Tanaka, 1995), where the Viking 1 Lander and Mars 

Pathfinder sites occur (*, Golombek and others, 1997; Crumpler 

and others, 2001).

Regionally focused, long-lived volcanism resulted in the 

formation of high-standing and broad rises and shields, plateaus, and local edifices. The Tharsis rise (or region) consists 

of an immense assemblage of flow fields that extend 5,000 km 

east-west by 6,000 km north-south. The rise is capped by some 

of the largest volcanic constructs in the solar system, including Olympus Mons, Alba Mons, and the three aligned Tharsis 

Montes (Ascraeus Mons, Pavonis Mons, and Arsia Mons). In 

addition, the Tharsis rise includes fields of smaller volcanoes, 

as well as tectonically deformed, elevated terrains that include 

parts of Tempe Terra, Noctis Fossae, Claritas Fossae, Ceraunius 

Fossae, and the Thaumasia highlands (*, Tanaka and others, 

1991; Dohm and others, 2001a). The summit of Olympus Mons 

stands at 21,229 m—the highest elevation on Mars—and the 

mountain is surrounded by several blocky, lobate aureoles that 

extend for hundreds of kilometers. Other regional volcanic centers include the Elysium rise (composed of Elysium Mons and 

surrounding volcanoes and lava-flow fields), Hesperia Planum 

and Malea Planum (northeast and southwest margins of Hellas 

Planitia, respectively), and Syrtis Major Planum (west margin 

of Isidis Planitia). Smaller volcanoes and volcano-like edifices 

ranging from tens to a few hundred kilometers in diameter are 

distributed across the southern highlands, with a particular concentration south of the Tharsis rise. 

Both of the Martian poles are capped by plateaus that are 

elevated a few kilometers above the surrounding plains. The 

circular, north polar plateau—Planum Boreum—occurs near 

the geographic center and low point (approx. –5,000 m elevation) of the northern lowlands. Planum Boreum is ~1,000 km in 

diameter and is partly surrounded by vast dune fields, including 

Olympia Undae. The south polar plateau—Planum Australe—

occurs within southern cratered highlands standing at 1,000 to 

1,500 m elevation. Planum Australe has an ellipsoidal planimetric shape (~1,100 x 1,400 km). Both poles contain characteristic spiral troughs that expose the depths of the polar plateau, 

2Table D1 is a Microsoft Excel spreadsheet file in .xlsx format available 

online only. This table provides a more complete presentation of the crater 

size-frequency data and results for the same 48 counting areas provided in 

table 2. The additional information includes total numbers of craters; whether 

a resurfacing correction was used; diameter ranges used for model crater sizefrequency fits; numbers of craters in fit ranges; cumulative densities and density 

errors of craters >1 km in diameter per million km2 for model-fit isochrons; 

actual cumulative crater densities for diameter steps at 0.5, 1, 2, 5, and 16 km; 

ratios of actual to expected values of cumulative densities, based on estimated 

densities projected from values at next larger diameter step; instrument that 

obtained the image data used; image numbers; and image resolutions.
3

including one large reentrant in the north (Chasma Boreale) 

and three reentrants in the south (Chasma Australe, Promethei 

Chasma, and Ultimum Chasma).

Data

The primary base maps for this geologic mapping investigation are the Mars Global Surveyor (MGS) Mars Orbiter Laser 

Altimeter (MOLA) digital elevation model (DEM) (463 m/

pixel resolution at lower latitudes to 115 m/pixel near the poles) 

(Smith and others, 2001) and the Mars Odyssey (ODY) Thermal 

Emission Imaging System (THEMIS) daytime infrared (IR) 

image mosaic (100 m/pixel) (Christensen and others, 2004). 

Both data sets are registered to the spheroid of Mars, with an 

equatorial radius of 3,396.19 km and a polar radius of 3,376.2 

km (Seidelmann and others, 2002). Longitude increases to the 

east, and latitude is planetocentric, in compliance with IAU 

(International Astronomical Union), International Association 

of Geodesy, NASA (National Aeronautics and Space 

Administration), and U.S. Geological Survey standards.

The MOLA-derived shaded-relief image used for the base 

represents more than 600 million single altimeter measurements 

gathered between 1999 and 2001, adjusted for consistency 

(Smith and others, 2001; Neumann and others, 2001, 2003), 

and converted to planetary radii values. Using these values, 

elevations above the areoid were determined from the Martian 

gravity field solution GMM-2B (Lemoine and others, 2001). 

The average accuracy of each point is originally ~100 m in horizontal position and ~1 m in radius (Neumann and others, 2001). 

However, the total elevation uncertainty is at least ±3 m due to 

the global error in the areoid (±1.8 m according to Lemoine and 

others, 2001) and regional uncertainties in its shape. The measurements were converted into a digital elevation model (DEM; 

Neumann and others, 2001) using Generic Mapping Tools software, with a resolution of 128 pixels/degree (or 463 m/pixel at 

the equator). The MOLA DEM does not contain data at lat >88° 

N. and S. due to the 92.8° inclination of the MGS orbit (Smith 

and others, 2001).

A shaded-relief image was generated from the DEM with a 

sun angle of 45° from horizontal and a sun azimuth of 335°, as 

measured clockwise from north. 

The artificially illuminated MOLA DEM serves as the 

base for the printed geologic map. To provide a true global 

view on a single map sheet, Robinson projection was selected 

at 1:20,000,000 scale. Polar regions (lat >70° N. or S.) are 

represented in stereographic projection. The printed map scale 

forms the basis for determining the digital mapping parameters 

and the minimum size of mappable features, as discussed in the 

Mapping Methods section.

The THEMIS daytime and nighttime IR 100 m/pixel 

global mosaics (version 11; P.R. Christensen, N.S. Gorelick, 

G.L. Mehall, and K.C. Murray, THEMIS Public Data Releases, 

Planetary Data System node, Arizona State University, http://

themis-data.asu.edu) represent thermal infrared energy emitted in nine wavelength bands, which relate to the temperature and emissivity of the surface (Christensen and others, 

2004; Edwards and others, 2011). For the daytime mosaic, 

about 21,000 THEMIS daytime images were selected with 

the following parameters: shutter closing time <150 seconds, 

incidence angle <85°, minimum surface temperature >160 K, 

and 0 percent saturated pixels from lat 90° S. to 90° N. with 

unsummed (full-resolution) data. For the nighttime mosaic, 

images were selected with the following parameters: shutter 

closing time <150 seconds, incidence angle >95°, minimum 

surface temperature >160 K, and 0 percent saturated pixels from 

lat 75° S. to 75° N. with unsummed data. The daytime mosaic 

covers ~95 percent of the planet, with data gaps most common 

between lat 50° and 70° N. The daytime data are generally 

indicative of morphology, as temperature variations are dominated by surface orientations relative to solar incidence. The 

THEMIS IR nighttime mosaic covers the region within lat ±60° 

and has some missing data at the highest latitudes, resulting in 

about 80 percent total coverage of the planet. Nighttime IR data 

represent the thermal inertia of the surface materials, showing 

that brighter materials have cooled less and, thus, are likely 

composed of coarser-grained materials, indurated surfaces, and 

(or) bedrock (*, Fergason and others, 2006; Putzig and Mellon, 

2007). These data were used to assist in discriminating contacts 

in regions where the intrinsic thermal inertias of map units were 

not overly obscured or altered (Christensen and others, 2004). 

Initial geologic mapping results using the base maps were 

verified and honed through integrating other data sets, including MOLA-derived products (especially color-shaded-relief 

and slope-detrended maps) and local, higher-resolution images 

via web-linked image footprints using geographic information system (GIS) software. Where available, higher-resolution 

images provided important information regarding unit texture 

and stratigraphic relations. In some instances, THEMIS visual 

range images (18 to 36 m/pixel) (Christensen and others, 2004) 

and Mars Reconnaissance Orbiter (MRO) Context Camera 

(CTX) images (5 to 6 m/pixel) (Malin and others, 2007) were 

consulted where THEMIS IR data are lacking or where identification of small features and textures on scales of tens of meters 

was required to confirm unit characteristics and to determine 

and (or) refine contact locations and stratigraphic relations. 

Other spacecraft data sets (for example, spectral and radar 

sounding) were not directly used for geologic mapping. Rather, 

we consulted and implemented published topical investigative 

results that relied on these types of data, as noted through citation, to help characterize and interpret map units and features 

and their relations that pertain to global geologic history. 

Mapping Methods

Photogeologic mapping methods that are routinely 

employed to identify geologic units on Mars have a heritage in 

approaches applied to remotely sensed image and topographic 

data acquired through terrestrial and lunar sensors (*, Wilhelms, 

1990; Smith and Pain, 2009). Geomorphic characteristics not 

only can be recognized in such data, but they generally are 

more ubiquitous, mappable, and interpretable with respect to 

the type, timing, and physical modification of bedrock geologic 
4

materials than are compositional signatures and other data sets. 

The latter primarily reveal surficial information or very low 

resolution geophysical data that pertain to buried materials and 

structures (though all existing information informs on aspects 

of the geology of Mars). Geomorphic characteristics that are 

most useful to geologic mapping include stratigraphic relations 

(for example, layers, layer truncations, and unit embayments 

and (or) burial), lithologic properties (for example, impact, 

mass-wasting, and volcanic morphologies), and modificational 

features (for example, tectonic, fluvial, and periglacial landforms). In addition, terrestrial photogeologic mapping studies 

based on simulated planetary data sets have applied ground 

truth to test the reliability of planetary photogeologic mapping 

approaches (*, Tanaka and others, 2009; Skinner and Fortezzo, 

2013), leading to a conservative and defensible methodology 

that we employ here. With some minor refinement to defining 

crater-density boundaries (Werner and Tanaka, 2011; Michael, 

2013), the eight-epoch chronology system of Tanaka (1986) is 

employed in the current map.

Map Development and Author Roles

The methods described in the following subsections chiefly 

result from (1) our collective experience mapping Mars (*, Scott 

and Tanaka, 1986; Tanaka and Scott, 1987; Dohm and others, 

2001a; Tanaka and others, 2005; Skinner and Herkenhoff, 2012; 

Tanaka and Fortezzo, 2012; Irwin and Grant, 2013); (2) the state 

of the art in handling global mapping data sets using digital 

mapping technologies (see below); (3) methods used in recent 

terrestrial geologic maps at global (*, Bouysee, 2009) and continental (*, Reed and others, 2005) scales; (4) guidance provided 

by the Geologic Mapping Subcommittee of NASA’s Planetary 

Geology and Geophysics Program and its Planetary Geologic 

Mapping Handbook (Tanaka and others, 2010); and (5) the 

application of the interrelated, guiding principles of consistency, 

simplicity, clarity, utility, and communicability as chosen by our 

mapping team. 

The production of a global map necessitates spatial and 

categorical generalization of geologic units and features that 

would otherwise be mapped in more detail at larger scales 

(*, Varnes, 1974). These generalizations can be accommodated 

at the selected map scale by carefully balancing cartographic 

symbols and geologic descriptions. However, unlike many 

terrestrial examples of small-scale geologic maps (*, Bouysee, 

2009), the map presented herein represents original mapping 

work, augmented with a variety of published topical science 

investigations, rather than the compilation and generalization of 

multiple larger-scale geologic map products.

The initial mapping of units and features by region was the 

responsibility of four of the authors: Tharsis region and Argyre 

basin (Dohm), northern lowlands and Arabia Terra (Skinner), 

southern highlands (Irwin), and south polar region and Hellas 

basin (Kolb). To establish consistency, the global-line-feature 

mapping and contact attributing were later given to a single 

mapper (Fortezzo). The entire map was edited and compiled under the direction of the lead author (Tanaka) through 

iterative reviews with primary mappers as well as mapping 

team discussions, when the schemes for unit naming, grouping, 

and coloring, as well as for contact and line-feature attributing 

were developed. Outcrop unit assignments were based partly 

on age, which required determination of high-accuracy, local 

crater-density ages of type localities (Platz and Michael). To 

assist in global unit and outcrop age assignments, we compiled 

cumulative crater densities for all unit occurrences through a 

global crater database (Robbins and Hynek, 2012) (see Age 

Determinations section below). Data management and validation and GIS software oversight (Hare) ensured spatial accuracy 

and efficiency in mapping.

Unit Delineation

Map units identify temporally unique geologic materials 

of substantial thickness and extent for portrayal at map scale. 

Identifying characteristics that establish geologic uniqueness include primary (formational) morphology, IR brightness 

(daytime or nighttime), and (or) albedo characteristics from 

visual-range-image data, stratification, relative age, and spatial 

geologic associations, which are described in the Description 

of Map Units. Primary characteristics and landforms in this 

map include lobate scarps (identifying flow boundaries within 

or at the margin of a unit), layering (presence and thickness 

of layers), dunes, plains, and shields and cones (indicative of 

volcanic vents). The primary versus secondary (modificational) 

nature of some morphologic features is uncertain, and defining 

units using secondary features was avoided (although they were 

commonly helpful in establishing time gaps between adjacent 

units, as well as typical modification history; they are noted in 

the additional characteristics column in the Description of Map 

Units). Our unit delineation approach thus differs from the previous global geologic maps of Mars, which included secondary 

morphologic and albedo features among the principal attributes 

of map units. For the Noachian units, we did not delineate 

Noachian crater ejecta within them, as shown in many other 

Mars geologic maps (*, Scott and Carr, 1978; Scott and Tanaka, 

1986), because of the difficulty in many cases of identifying the 

limit of the ejecta plus the fact that most Noachian materials are 

interpreted to include impact ejecta.

Units are delineated by relative age as borne out by 

stratigraphic overlap and embayment relations, and their 

chronostratigraphic ages were determined by the densities of 

impact crater populations. Units were assigned ages according 

to the three periods previously defined by Scott and Carr (1978) 

and the eight epochs that the periods were later divided into by 

Tanaka (1986). Many units are likely to consist of complexly 

intermixed materials of contrasting age and provenance. Such 

intercalations are neither consistently observable nor possible 

to represent using regional to global data sets and small map 

scales. We ignored surficial materials that are estimated to 

be meters thick (or smaller), including dust, duricrust, desert 

pavement, and icy soils and mantles (*, Mustard and others, 

2001; Putzig and Mellon, 2007). These generally are too thin to 

recognize and map at global scale. An exception is the approximately meter-thick Amazonian polar cap unit that constitutes 
5

distinctively bright, mappable surfaces in the polar regions 

(*, Langevin and others, 2005; Tanaka and Fortezzo, 2012). 

Because of improvements not only in data resolution and quality but also in mapping approaches and thoroughness of crater 

dating, many unit exposures have improved age assignments 

with more consistent accuracy compared to those of the Vikingbased global map (Scott and Tanaka, 1986; Greeley and Guest, 

1987; Tanaka and Scott, 1987).

Unit Groups

Global and continental scale maps of Earth are necessarily made up of broadly inclusive units that can be grouped 

naturally, given their composition and (or) geographic occurrence. For example, in the “Geological Map of the World” 

(Bouysee, 2009), onshore and offshore areas make up the major 

unit groups, each consisting of lithologic divisions. Also, in the 

“Geological Map of North America” (Reed and others, 2005), 

materials are grouped lithologically as sedimentary, volcanic, 

plutonic, metamorphic, and undivided crystalline rock types. 

Both of these maps further divide the lowest-rank groups into 

units according to chronostratigraphic age.

Similarly, we employ a unit grouping scheme that uses 

both geographic setting and lithologic divisions for unit names 

and labels. Geographic setting consists of highland, lowland, 

transitional, basin, polar, and apron groups, all containing multiple units subdivided primarily by age and, in some cases, primary morphologic character. The lithologic units are composed 

of volcanic and impact (crater) categories. All groups (except 

the globally distributed impact unit) coincide closely with major 

geographic zones (see Physiographic Setting), and some groups 

typically have either low or high kilometer-scale roughness 

(Kreslavsky and Head, 2000; see Description of Map Units). 

In contrast, the previous Viking-based global geologic map 

included formations and assemblages that, in some cases, distinguished materials of similar origin and age but were associated 

with a particular geographic feature that was incorporated into 

the name. The post-Viking geologic map of the northern plains 

of Mars (Tanaka and others, 2005) dispensed with formation 

names for units but still incorporated geographic nomenclature in many unit names. Thus, the new map presented here is 

closer to the approach used in the original, Mariner 9-based map 

that grouped 24 geomorphic units (lacking formal geographic 

names) into 5 terrain types.

Unit Names and Labels

Unit names and labels consist of the following components: (1) age, (2) unit group, and (3) subtype (optional). For the 

first time in a map of Mars, the age assignments are included in 

the unit names to the precision of epochs where possible. This 

approach is consistent with approaches used in most terrestrial 

geologic maps (*, Reed and others, 2005; Bouysee, 2009). 

Moreover, the approach elevates the prominence and statistical 

integrity of crater-density dating efforts applied to map units, 

which is one of the most significant advancements resulting 

from this map. The interpreted age of each geologic unit is 

identified in the unit label, where capital letters show the stratigraphic period (N, Noachian; H, Hesperian, A, Amazonian) and 

epoch is denoted by the use of a preceding lower-case letter (e, 

Early; m, Middle; l, Late). Where units include more than one 

epoch within a period, the epochs are not discriminated in the 

unit names and labels—the Correlation of Map Units (CMU) 

specifies the interpreted epoch range. In a few cases, observed 

superposition relations noted in the Description of Map Units 

(DMU) can be more precisely defined than shown in the CMU, 

which does not portray temporal relations within epochs. In 

addition, for units spanning more than one Martian period, 

the youngest period is followed by the oldest in the unit label 

and name (for example, HN, Hesperian and Noachian). The 

unit group designation follows the age component in both unit 

labels and names (a, apron; b, basin; h, highlands; i, impact; l, 

lowlands; p, polar; t, transition; v, volcanic).

In some instances, we needed to discriminate particular 

unit subtypes. Hence, the first letter of a modifying word follows unit group names and labels (c, cap; d, dune; e, edifice; 

f, field; m, massif; o, outflow; u, undivided). The term, “cap”, 

represents high-albedo, residual ice sheets that cover parts of 

the polar plateaus. Dune refers to typical yet diverse (barchan, 

linear, star, chained, and other complex shapes and patterns) 

eolian bedforms. Edifice represents topographic features consistent with volcanic construction. Field represents groups of 

relatively small (less than a few tens of kilometers across) volcanic vents and their contiguous lava plains. Massif represents 

especially rugged, high-relief, heavily cratered materials that 

typically form the rims of large impact basins. Outflow represents deposits that occur within—and are genetically linked 

to—large-scale outflow channels. Undivided units refer to 

layered sequences that may be hundreds of meters to kilometers 

thick; layering provides a basis for potential stratigraphic divisions in larger-scale mapping, particularly where unconformities and (or) lithologic changes can be identified. For example, 

the Amazonian polar undivided unit (Apu) is divided into four 

sequential units at 1:2,000,000 scale (Tanaka and Fortezzo, 

2012).

Contact Types

Contacts are shown as either certain (solid), approximate 

(dashed), or internal (solid with younger (y) and older (o) labels). 

Certain contacts are considered to be well defined by morphologic and (or) IR brightness/albedo boundaries at digital mapping 

scale (1:5,000,000). Approximate contacts are imprecise due to 

weakly evidenced, obscured, gradational, and (or) complex unit 

boundaries. We identified internal contacts within Late Hesperian 

and Late Amazonian volcanic units (lHv and lAv, respectively), 

where one flow field overlaps and postdates another, and within 

some occurrences of unit AHv, where the ejecta of one crater 

overlaps that of another. In places, high-resolution images were 

used to augment global MOLA and THEMIS daytime IR base 

maps for contact mapping. For example, CTX images were 

locally used to verify and refine the contact between Amazonian 

and Hesperian transition undivided units (AHtu and Htu), based 

on recognition of relatively small landforms. Given the mapping 
6

scale and smoothing applied to the drafted linework, extensive 

cartographic generalization occurs in which the detailed form of 

complex contacts evident at larger scale has been subdued or lost 

at the 1:20,000,000 map scale.

Line Feature Types

Our map includes line features categorized by major 

geologic types based on their typical morphologic forms (see 

Explanation of Map Symbols). The cartographic nature of this 

global product necessitates balanced spatial representation, 

rather than thorough identification of morphologic and tectonic 

features. Major feature types are classified according to preservation state (fresh, subdued, partly buried, or buried) and width 

(greater than or less than 10 km) in the digital map product (see 

map feature GIS attribute table for width designations). 

Wrinkle ridges generally indicate tectonic contraction 

resulting from deep-seated (several kilometers or more) thrust 

faulting (*, Golombek and others, 2001). Broad grabens (>10 

km wide) indicate deep-seated rifting (*, Hauber and others, 

2010), whereas narrow grabens are indicative of either hourglass-configured normal faults (*, Schultz and others, 2007) 

or shallow detachment along horizontal mechanical interfaces 

that may be underlain by dikes or hydrofractures (*, Tanaka 

and others, 1991; Grosfils and Head, 1994). Outflow channels 

likely formed as the result of catastrophically erupted, pressurized groundwater (*, Baker and others, 1992), whereas narrow 

valleys likely formed through outburst floods and (or) precipitation-driven surface runoff (*, Howard and others, 2005). (See 

Hynek and others, 2010, for more detailed mapping of valleys.) 

In some cases, mass flows, glaciers, and lava flows may also 

be responsible for channel formation, and rilles form a specific 

channel type that generally narrows downslope and is attributed mainly to thermal erosion (*, Nummedal and Prior, 1981; 

Lucchitta, 1982; Leverington, 2011). Ridges and scarps, where 

diagnostic morphologic associations are absent, may result from 

a variety and combination of geologic processes, including tectonic and impact deformation; fluvial, glacial, and mass-wasting 

erosion; and volcanism (*, Anderson and Anderson, 2010). 

Spiral troughs are particular erosional features related to erosion 

and transport of the polar plateaus by insolation and katabatic 

winds (*, Howard, 1978, 2000; Smith and Holt, 2010). Flow 

directions are mapped to show major trends of volcanic flows. 

Crater rims >100 km in diameter are drawn where regionally 

prominent, but possible buried craters (including quasi-circular 

depressions of Frey, 2006) suggested by tectonic features and 

shallow circular depressions are excluded. Some impact craters 

include circular, partial to complete peak rings within them, 

which are mapped as ridges (Lyot, Lowell, and Schiaparelli). 

Locally, pit crater chains occur where subsurface excavation 

led to collapse, likely related to dilational faulting and fissuring 

and possibly enhanced locally by groundwater flow (*, Wyrick 

and others, 2004). Rims of volcanic calderas >100 km across 

indicate sites of large-scale magma-chamber collapse, associated with effusive flank eruptions and central explosive eruptions, and are identified on the largest volcanic edifices of Mars 

(*, Crumpler and others, 1996; Williams and others, 2009).

Drafting 

We used the Environmental Systems Research Institute, 

Inc. (Redlands, CA) ArcGIS software package to co-register 

and analyze available datasets. Simple Cylindrical versions of 

MOLA and THEMIS IR mapping bases were created in lossless 

GeoJPEG2000 format. For consistency and legibility at map 

scale, we defined drafting parameters within our digital GIS 

environment. First, the vertex spacing of drafted linework was 

set at 5 km (4 vertices per millimeter at 1:20,000,000 scale), 

which provides sufficient detail and curve rounding when a 

smoothing algorithm is applied to the linework. We drafted 

linework while viewing the map base data at 1:5,000,000 scale 

to ensure sufficient accuracy at print scale. The minimum linefeature length is 100 km, and the minimum outcrop dimensions 

are 40 km wide by 100 km long for legibility. Given differences 

between drafting and production scales, we avoided mapping 

narrow outcrops using parameters consistent with our minimum width specifications. Minimum spacing between linework, including both contacts and other line features, is 40 km. 

However, we exercised some flexibility in the size and spacing 

cutoffs to represent critical geologic and stratigraphic relations, 

including some narrow wall rock outcrops of Valles Marineris. 

Also, we generalized some segmented, en echelon grabens that 

were too short to map as single segments by mapping them as 

single collective features to show the occurrence of particular 

structural fabrics.

Line symbols were adapted from standard drafting conventions (Federal Geographic Data Committee, 2006). In general, 

units within groups were assigned to color families (yellow for 

the impact unit; greens for lowland units; blues for polar units; 

bluish greens for basin units; reds, oranges, and purples for 

volcanic units; and browns, oranges, and gray tones for apron, 

transition, and highland units). This approach is similar to that 

used in previous Martian global map-unit color schemes (Scott 

and Carr, 1978; Scott and Tanaka, 1986).

Age Determinations

The relative age of each map unit was determined using 

the scheme of three chronostratigraphic periods and eight epoch 

divisions of the periods that are based on the crater densities 

of key referent surfaces (table 1; Tanaka, 1986; Werner and 

Tanaka, 2011). Detailed crater size-frequencies were obtained 

for representative counting localities for 23 of the 44 map units 

(table 2 and fig. 1) primarily from HRSC (High Resolution 

Stereo Camera, onboard the Mars Express spacecraft) data at 

12.5 m/pixel and secondarily CTX data at 5 to 6 m/pixel using 

the GIS extension CraterTools (Kneissl and others, 2011) and 

the Craterstats software (Michael and Neukum, 2010). Selection 

of representative counting localities was required, because (1) 

the total areas and numbers of craters of specific units were 

too large for complete counts, (2) many of the units exhibited 

diverse or modified morphologies and other characteristics that 

made dating areas displaying the most typical morphologies 

the most desired, (3) parts of unit surfaces have been modified 
7

by erosion, tectonism, deposition followed by exhumation, and 

other resurfacing processes that would also result in atypical 

crater populations (and thus avoided), and (4) some areas had 

inadequate, high-resolution (HRSC and CTX) image coverage 

(for a more thorough treatment, see Platz and others, 2013). 

In some cases, pertinent crater counts that adequately date the 

units have been published and are cited where the units are 

described in the Geologic History section for comparison with 

(or in lieu of) crater counts in this map (tables 2, 3, and D1). For 

some units having great durations as established by stratigraphic 

relations, high degrees of post-emplacement crater obliteration, and (or) wide variations in crater densities, detailed crater 

counts are not helpful in constraining their ages and thus were 

not obtained. 

Model ages derived from the Hartmann and Neukum 

(2001) chronology function are based on the Ivanov (2001) 

crater production function. Parts of the crater size-frequency 

distributions that fit well to the production function over continuous ranges of diameter were used to determine model ages. 

The Craterstats software performs adjustments that allow for 

the fitting of multiple resurfacing ages at progressively smaller 

diameter craters. Thus, many counts resulted in two or more age 

populations (table 2). Each crater count was tested for spatial 

randomness to avoid surfaces where crater populations may 

have been affected by secondary craters or by inhomogeneous 

resurfacing (Michael and others, 2012). 

Because of their widespread occurrence and role in establishing global stratigraphy, we focused much of our attention on 

the stratigraphic differentiation of Noachian highland unit outcrops, wherein our mapping identified three morphologic-chronostratigraphic categories: (1) Early Noachian—highest relief 

and highest density of impact craters, (2) Middle Noachian—

moderate relief and intermediate density of impact craters, and 

(3) Late Noachian—low local relief and relatively low density 

of impact craters. Although contacts between these units generally are not sharply defined, most follow topographic breaks 

where surface landforms become embayed, buried, and (or) 

markedly subdued. Where counts of all impact craters (including buried and otherwise modified craters) yielded multiple 

surface ages, the nature of the unit being dated was specifically 

assessed to determine the most appropriate age. For example, 

model age determinations for Early Noachian units were applied 

to the oldest crater-retention ages, whereas model ages of some 

younger units were applied to a younger resurfacing age in the 

crater distribution. This assumption was verified by examining the appearance of the actual craters being counted. In most 

instances, we confirmed that buried crater populations pre-date 

the unit. Moreover, we were able to verify that the ages that we 

had suspected for these and other stratigraphically significant 

units were generally correct in the representative areas, which 

verified our stratigraphy. Once we verified that the epoch and 

period crater-density boundaries of Tanaka (1986) and Werner 

and Tanaka (2011) were still valid when applied to this new 

map, we then could use crater counts to verify or reassign the 

unit designations for otherwise equivocal outcrops.

Given the above analysis, we now define the Early, 

Middle, and Late Noachian highland units as new referents 

for their respective epochs, thus revising those ages based on 

the previous Viking-based maps of Mars (Tanaka, 1986). We 

have similarly defined new referent units for the Hesperian 

and Amazonian epochs (table 1), which for the Hesperian have 

heritage to previously used referents (Tanaka, 1986). The Early 

Hesperian Epoch is defined by the Early Hesperian volcanic 

unit (eHv), which includes materials of volcanic plains in 

Hesperia Planum on which the Hesperian Period definition was 

founded (Scott and Carr, 1978). The unit also includes broad 

volcanic flow fields spread around the Tharsis region, as well as 

making up Syrtis Major Planum. The Late Hesperian lowland 

unit (lHl) defines its epoch, following the precedent of Tanaka 

(1986). A new Early Amazonian referent is the areally small 

Early Amazonian basin unit (eAb)—the only map unit confined 

to this epoch in spite of the epoch’s apparent approximately 

2-b.y. duration (table 1). Similarly, only the Middle Amazonian 

lowland unit (mAl) occurs solely within its epoch. Finally, a 

new referent for the Late Amazonian is the Amazonian polar 

undivided unit (Apu), which forms ice-rich layered plateaus at 

both poles (commonly referred to as “polar layered deposits”). 

Although the base of this unit is poorly defined, it significantly 

contains a record of recent climate variation on Mars.

Our approach to crater counting was limited to representative locations ranging in size from 4 x 103

 km2 to 90 x 103 km2, 

where all observed craters were counted down to minimum 

diameters of between 100 to 400 m depending on the area size 

and surface age (presented in detail by Platz and others, 2013; 

see also table 2 and fig. 1 showing areas counted). For most of 

these locations, we determined two model ages (in other cases, 

one or three). The older age based on the largest craters present 

was often assigned as unit formation age to ancient highland 

and thick volcanic units. The reported resurfacing age is also 

provided to highlight that surfaces experienced post-formation 

modification through erosion, deposition, deformation, or 

impact cratering. For younger units that do not completely bury 

older surfaces, the resurfacing age has been used to infer unit 

formation ages (for example, at locality 34 in table 2 and fig. 1, 

the mapped Late Noachian highland unit, lNh, buries an Early 

Noachian surface). The older ages reported in those cases correspond to the ages of underlying units that were partly buried 

by the young surface of interest. Although craters were counted 

to minimum diameters between 100 and 400 m, the minimum 

diameter used to fit the isochrons was generally ≥400 m (in 

four instances the minimum diameter was between 200 and 

350 m).

We also excluded visible clusters, chains, and strewn 

fields of secondary impact craters from the counting area. Each 

measured crater size-frequency distribution was also tested for 

spatial randomness using the procedure of Michael and others 

(2012) and discarding any that were not sufficiently random 

(see also Platz and others, 2013). 

Remaining outcrops were too large (some exceeding 100 

x 103 km2), too numerous, or otherwise problematic for counting craters approximately <1 km in diameter, and they required 

a simplified although less precise crater-dating approach. For 

these, we applied the global impact crater database that consists 

of all craters with diameters >1 km (Robbins and Hynek, 2012). 
8

This database was imported into our GIS project, enabling automatic generation of cumulative crater densities for the entire 

unit areas (including as needed assimilation of superposed unit 

AHi outcrops), as well as individual occurrences that could be 

compared with the assigned and calculated boundary densities for craters >1 km (N1), >5 km (N5), and >16 km (N16) in 

diameter that define epoch boundaries (table 3). This approach 

required merging the Amazonian and Hesperian impact unit 

(AHi) into subjacent units, which allowed proper inclusion 

of the impact craters that define unit AHi. This exercise was 

performed for all units where unit AHi occurrences were 

superposed.

Our representative counts of the Middle Noachian highland 

unit (table 2 and fig. 1; see also Platz and others, 2013) indicate 

that craters >10 km in diameter have been preserved, validating 

our application of N(16) values to discriminate most surfaces 

for their relative age to the upper and lower boundaries of the 

Middle Noachian. For the Late Noachian/Early Hesperian and 

Early Hesperian/Late Hesperian boundaries, N(5) was more 

accurate based on the statistical preservation of craters larger 

than this diameter. Though most Amazonian surfaces display 

craters preserved down to 1 km diameter, some potentially 

Early Amazonian surfaces of unit AHtu are missing craters as 

large as 5 to 6 km in diameter due to mass wasting and erosion. Most outcrops in our initial mapping had an N(1), N(5), 

or N(16) value that corresponded with the age of the unit to 

which they were assigned. Where the crater density was in clear 

disagreement with the initial age assignment, the outcrop was 

re-assigned to a morphologically similar unit whose age was 

in agreement with the outcrop (for example, switching a unit 

designation from eNh to mNh or eHv to lNv based on crater 

density). This procedure commonly resulted in the merging 

of adjacent outcrops that had the same unit designation. Some 

outcrops do not contain crater populations that yield statistically 

meaningful crater densities. In these instances, direct craterdensity dating is not well constrained, although crosscutting and 

overlap relations with adjacent units helped to establish meaningful stratigraphic assignments. 

Crater populations for many Late Noachian and younger 

surfaces include topographically subdued, often rimless craters 

that likely belong to buried surfaces. Thus, we did not include 

such craters when deriving crater densities from the global 

crater data base in order to obtain accurate ages. We recognize, 

though, that the unit surface age provides only a minimum age 

constraint, whereas older age constraints come from the ages 

of surfaces buried or embayed by the unit. In some cases, such 

as for the Late Hesperian lowland unit (lHl) and the Amazonian 

and Hesperian volcanic edifice units (Ave and Hve, respectively), the oldest parts of the units are buried, which means that 

the age of initiation of unit emplacement is unconstrained. To 

show this lack of constraint, the lower edges of the unit boxes 

have sawtooth-edged age boundaries in the CMU. In addition, 

some transition units have two major, inseparable components 

of different age—combinations of Noachian highland material and Hesperian or Amazonian plains or apron material. 

The age ranges for these units span the development of both 

components. 

When dating impact craters and basins >150 km in diameter, our results are generally consistent with those of Robbins 

and others (2013), who dated 76 of the 102 features that they 

identified in this size range. We have dated nearly all of the 

features using stratigraphic and geomorphic observations (table 

4), crater densities (tables 2 and 4), and other work (noted in 

table 4). The identification, measurement, and dating of 28 

craters are considered to be moderately to highly uncertain 

(these are marked with an asterisk in table 4), and one crater is 

now considered to be in error (S.J. Robbins, written commun., 

2013). Some discrepancies result, particularly for features that 

we assigned Late Noachian and younger ages, given how the 

crater extents were mapped and (in our approach) the number of 

craters identified within and superposed upon the crater ejecta. 

In addition, Robbins and others (2013) determined ages based 

on diameters >10 km to fit to absolute-age schemes, whereas 

we used craters >5 and >16 km in diameter to determine epoch 

ages. For example, the mapped extent for Galle crater includes 

the continuous ejecta, whereas Robbins and others (2013) dated 

only the rim of Galle. We find 7 to 9 superposed craters >5 km 

diameter (the relative positions of two craters are equivocal), 

yielding an N(5) density of 43±16 to 55±18 that corresponds 

most likely to the Early Amazonian (Werner and Tanaka, 2011). 

The method of Robbins and others (2013) yielded a median 

age within the Late Noachian. The ejecta of Galle overlie the 

Hesperian and Noachian basin unit covering Argyre Planitia, 

which has a distinctly higher density of craters (N(5) = 209±25, 

indicating a Late Noachian or Early Hesperian age).

Many outcrops, particularly of Middle and Late Amazonian 

units, could not be accurately dated using craters larger than 1 

km. However, in some cases, published crater counts of smaller 

craters for these units exist and were utilized for our age designations (*, Vaucher and others, 2009; Hauber and others, 2011; 

Skinner and others, 2012). Other outcrops and units have been 

eroded, mantled, or otherwise obscured to the point that crater 

densities are not indicative of unit age. Post-Noachian impact 

craters are generally identified and mapped based on the relatively pristine morphologic expression of their rim and ejecta but 

are too numerous to date individually. As such, they are grouped 

into a single Amazonian and Hesperian impact unit (AHi). The 

vast lava-flow fields comprising most of the central extents of 

the Tharsis and Elysium rises show ranges of ages and pathways of individual flows and local flow fields, commonly with 

no distinct separations of mappable areas of flows of different 

epochs. In such cases, we map the flows conservatively as the 

Amazonian and Hesperian volcanic unit (AHv), although previous mapping distinguished multiple flow units based on their 

mean crater densities (Scott and Tanaka, 1986). 

In summary, assignment of relative ages to the map 

units has been performed to the precision of the eight 

time-stratigraphic epochs of Mars (Tanaka, 1986; table 1), as 

shown in the Correlation of Map Units. These assignments are 

based on (1) stratigraphic relations revealed by the map, as well 

as (2) crater size-frequency data provided herein and from other 

sources (table 5). Thus, the robustness of each age assignment 

varies according to the quality, quantity, and applicability of 

mapping results coupled with crater statistical data.
9

Geologic History

This global map builds upon previous mapping results 

and provides new findings and synthesizes other research 

regarding the geology of Mars, based largely on spacecraft 

data obtained since the late 1990s. The geologic map includes 

detailed stratigraphic relations and crater-density statistics 

that allow for the reconstruction of regional to global geologic 

events that shaped the surface of Mars. We provide interpretations of the processes that resulted in the present-day landscape of Mars, given our mapping-based analysis as well as 

other published work. Processes that have effectively modified geological units through temporally extended or punctuated resurfacing have resulted in a geologic and stratigraphic 

record that is both complex and only partly accessible through 

mapping. 

Noachian Period

The Noachian Period includes the oldest observed 

geologic activities and resultant units on the surface of Mars, 

effectively recording rapidly declining impact bombardment 

from the Early to Late Noachian Epochs (*, Tanaka, 1986; 

Hartmann and Neukum, 2001). As a consequence of impact 

cratering and concurrent degradation processes, primary 

morphologies tens to hundreds of meters in relief and smaller, 

including tectonic, volcanic, erosional, sedimentary, and impact 

landforms, were effectively destroyed—especially those that 

formed during the Early and Middle Noachian Epochs. An 

exception is strata exposed in eroded Noachian sequences, 

including areas of the highlands that contain dense arrays of 

channels, as well as the walls of Valles Marineris (unit Nhu). 

Valley systems (*, Craddock and Howard, 2002; Fassett and 

Head, 2008a; Hynek and others, 2010) are locally associated 

with basin-filling deposits (*, Fassett and Head, 2008b) and 

suggest the occurrence of distributed, unmapped, thin outcrops 

of fluvial sediments included in Noachian units. In addition, 

Noachian highland volcanic edifices (*, Hodges and Moore, 

1994; Xiao and others, 2012) suggest that highland materials 

include variable amounts of volcanic rocks. Noachian units 

also contain post-Noachian crater ejecta, which generally is 

included in the units except where we delineated outcrops >100 

km across of the Amazonian and Hesperian impact unit (AHi). 

Larger volcanoes mapped as the Noachian volcanic edifice unit 

(Nve) display crater ages indicative of multiple stages of activity (Werner, 2009).

The Noachian geologic record in the lowlands is 

largely unknown, except for a few degraded and fractured 

Noachian outcrops east of the Elysium rise and at Acidalia 

Mensa (mapped as the Hesperian and Noachian transition 

unit, HNt), the arcuate Acheron Fossae structure north of 

Olympus Mons (mapped as the Late Noachian highland unit, 

lNh), and unmapped, buried, and degraded crater forms that 

pre-date the Hesperian plains-forming materials (Frey and 

others, 2002). The highland-lowland transition zone has 

been modified due to erosion by liquid water, water-ice, 

wind, and gravity-driven processes (*, McGill, 2002, 2005; 

Tanaka and others, 2005; Dickson and others, 2008; Chuang 

and Crown, 2009; Fairén and others, 2011; Davila and 

others, 2013), as well as by endogenic-driven deformation 

(*, Phillips and others, 2001).

The Noachian is also characterized by the highest mean 

global erosion rates (Golombek and others, 2006) and formation of extensive valley networks possibly peaking in intensity near the end of the period (*, Howard and others, 2005; 

Irwin and others, 2005; Fassett and Head, 2008a,b; Hoke and 

Hynek, 2009; Hynek and others, 2010). Large impact and 

perhaps tectonic landforms that pre-date the Noachian appear 

to be preserved in the highlands and lowlands (*, Schultz and 

others, 1982; Nimmo and Tanaka, 2005; Andrews-Hanna and 

others, 2008), despite later burial and modification (*, Hiesinger 

and Head, 2000; Frey and others, 2002; Tanaka and others, 

2005). Large extensional and contractional tectonic structures, 

hundreds to thousands of kilometers long, including Phlegra 

Montes, Tanais Fossae, older structures of Claritas Fossae, and 

scarp- and ridge-bounded basins in Terra Cimmeria and Terra 

Sirenum, point to a changing landscape during the Early and 

Middle Noachian Epochs, prior to the major rise of the Tharsis 

region (*, Baker and others, 2007).

Noachian geological units typically have a spectral signature that indicates a high abundance of basaltic compositions, 

including iron- and low-calcium-bearing pyroxenes and olivine, reported to mark modest crustal differentiation (*, Bibring 

and others, 2005, 2006). Early and Middle Noachian rocks 

also contain phyllosilicates and chlorite, which are interpreted 

to have formed through aqueous alteration (*, Poulet and 

others, 2005; Murchie and others, 2009; Ehlmann and others, 

2011; Ody and others, 2012). Chloride salts within Middle 

Noachian to Early Hesperian highland units occur in some 

valleys and basins and are thought to be produced by evaporation of briny water that carved valley networks (*, Murchie 

and others, 2009; Osterloo and others, 2010). Change to a more 

acidic environment fueled by extensive volcanism and volatile 

release, such as related to incipient Tharsis rise development 

(*, Dohm and others, 2001b; Phillips and others, 2001), may 

explain the reduced signature of phyllosilicates beginning in 

the Middle to Late Noachian in highland and transition units, 

after which sulfate-rich layered deposits in Meridiani Planum 

(unit HNhu) formed (*, Bibring and others, 2006; Ehlmann 

and others, 2011). 

The Martian highlands display zones of intense crustal 

magnetization in Terra Cimmeria and Terra Sirenum. The magnetization patterns may correspond to some exposed Noachian 

rock outcrops and structures, possibly indicating dynamic 

crustal evolution prior to Tharsis rise development (Dohm 

and others, 2013). Also, magnetization is weak in the vicinity of large impact basins, the northern plains, and volcanic 

regions, indicating that thermal events erased the possibly more 

widespread magnetization of early crustal rocks (*, Acuña and 

others, 2001; Connerney and others, 2001; Langlais and others, 

2004). Thus, the Martian magnetic field apparently disappeared 

prior to the majority of the Early Noachian geomorphic and 

geologic record, including Hellas basin (*, Nimmo and Tanaka, 

2005; Frey, 2006).
10

Early Noachian Epoch

The oldest crust on Mars consists of Early Noachian 

materials and inferred, buried pre-Noachian materials associated with topographically subtle basins that may be vestiges 

of impacts. These materials largely postdate formation of the 

broad northern lowlands, which comprise the earliest recognized geographic feature of the planet and are likely either 

of impact or tectonic origin (*, Nimmo and Tanaka, 2005; 

Frey, 2006; Andrews-Hanna, 2008). Our dating of the largest 

impacts in the global crater database of Robbins and Hynek 

(2012) indicates that the Early Noachian Epoch included 

formation of at least 65 impact basins that are >150 km in 

diameter (table 4; see also Werner, 2008; Robbins and others, 

2013). Eighteen of these basins are deeply buried or highly 

degraded and their identification, diameter, and age have 

greater uncertainty when compared to other basins. The largest 

basin is defined by Hellas Planitia (~2,400 km in diameter) 

and includes the lowest surface elevation on Mars. The Hellas 

basin, as an impact feature, includes an asymmetric (~5,000 

km in diameter northeast-southwest and ~6,000 km in diameter northwest-southeast) annulus of terrain elevated between 

1 and 2 km above the surrounding highlands, comprising a 

volume similar to that missing from within the basin (Smith 

and others, 1999). The interior and southeastern parts of the 

annulus are made up of massifs and intervening troughs and 

plains of the Early Noachian highland massif unit, eNhm, 

whereas remaining high-standing, rugged areas are the Early 

Noachian highland unit, eNh. The western and northwestern 

parts of the rim and annulus of Hellas basin are deformed 

by concentric and oblique ridges (Hellespontes Montes) and 

troughs (for example, Scylla Scopulus), which may have been 

the result of a low-angle impact directed southeast (Tanaka 

and Leonard, 1995). The ~1,160-km-diameter south polar 

basin is partly outlined by the Promethei Rupes scarp, which 

forms the extant basin rim and is largely buried by Planum 

Australe.

Outcrops of unit eNh in the remainder of the highlands 

are common east of Hellas basin in Terra Cimmeria and Terra 

Sirenum, corresponding to the zone of strong crustal magnetization, but are sparse around Argyre basin and in most highlands 

north of the equator in Arabia, Margaritifer, and Xanthe Terrae 

and northern Terra Sabaea. Some outcrops of unit eNh in the 

southern parts of the Tharsis rise contain dense arrays of linear 

to sinuous troughs interpreted to be narrow grabens and wide 

rifts, indicating crustal extension (*, Dohm and others, 2001a; 

Hauber and others, 2010). Other ridges made up of unit eNh

trending concentric to the margin of Daedalia Planum may have 

resulted from crustal contraction due to Syria Planum-centered 

uplift (*, Banerdt and others, 1992; Schultz and Tanaka, 1994). 

About two-thirds of mapped Noachian highland edifices (unit 

Nhe) and volcanic edifices (unit Nve) may be Early Noachian, 

which attests to early, widespread volcanism with a concentration south of the Tharsis region (Scott and Tanaka, 1981a; Xiao 

and others, 2012). Small valleys dissect Early Noachian units 

in places, and some fluvial dissection and mass wasting likely 

subdued prominent landforms during this epoch. Overall, Early 

Noachian materials consist mostly of impact breccias and melts, 

igneous rocks, and some sedimentary sequences.

Middle Noachian Epoch 

The Middle Noachian highland unit (mNh) dominates 

highland regions wherever the Early Noachian highland unit 

(eNh) is sparse or absent, including regions that border the 

highland/lowland transition zone in Arabia Terra and south of 

Elysium Planitia, as well as those that surround Argyre basin. 

Unit mNh also forms relatively low lying surfaces adjacent to 

higher-standing outcrops of unit eNh; commonly a slope break 

separates these units, wherein narrow (unmapped) valleys incise 

the steeper parts of the eNh unit. Unit mNh likely consists of a 

higher proportion of sedimentary and volcanic materials relative 

to unit eNh, which may reflect climate conditions conducive to 

precipitation and runoff (Irwin and others, 2013).

The highlands contain at least 15 Middle Noachian impact 

basins that are >150 km in diameter (table 4). Argyre and Isidis 

basins are regionally defined by topographic depressions surrounded by the Middle Noachian highland massif unit (mNhm). 

For Argyre basin, the massif unit has a mean outer diameter of 

~1,500 km and is surrounded by the Middle Noachian highland 

unit to a diameter of ~3,000 km. Unlike Hellas basin, this outer 

zone does not form a distinctly elevated annulus but includes 

broad, irregular troughs and ridges that are oriented mostly 

circumferential to the basin and that likely represent structural 

rings associated with basin formation. 

The Isidis basin is located along the highland/lowland 

transition and displays morphologic characteristics that are 

different than the similarly sized Hellas and Argyre basins. For 

example, Isidis basin has a discontinuous rim of the Middle 

Noachian highland massif unit (mNhm), which extends for a 

diameter of ~2,100 km and is interspersed with less rugged, 

lower-relief Middle Noachian highland unit (mNh) and postNoachian units. Circumferential, mostly narrow troughs 

encircle the northwest (Nili Fossae) and southeast (Amenthes 

Fossae) parts of the Isidis basin rim. The troughs likely formed 

through crustal extension during the Middle Noachian and 

were reactivated into the Hesperian, given that they locally cut 

the Early Hesperian transition unit (eHt). Oenotria Scopuli are 

basin-facing, circumferential scarps that displace and modify 

the Early Noachian highland unit (eNh) at a radial distance of 

1,400 to 1,500 km from the center of Isidis that appear to form 

a basin-ring structure. Carbonate, rare on the surface of Mars, 

occurs in a consistent stratigraphic horizon, in places surrounding Isidis basin, and reflects neutral to alkaline conditions at the 

time of formation, likely by alteration of an olivine-rich layer 

(*, Ehlmann and others, 2008); also, diverse assemblages of 

altered silicate minerals indicative of low-grade metamorphic or 

hydrothermal aqueous alteration occur in Noachian terrain west 

of Isidis basin (*, Ehlmann and others, 2009).

Noachian highland and volcanic edifices (units Nhe and 

Nve, respectively) are fewer in the Middle Noachian than in 

the Early Noachian, perhaps due to increased global compressional stress and crustal thickening, which restricted the ascent 

of magma away from regional magmatic centers such as Tharsis 
11

and Elysium (*, Xiao and others, 2012). Embayment by unit 

lNh shows that the Thaumasia highlands uplifted mostly during 

the Middle Noachian, and the development of densely spaced, 

narrow grabens and rifts across the Thaumasia highlands at this 

time indicates their contemporaneity with the uplift (Dohm and 

others, 2001a; Hauber and others, 2010).

Late Noachian Epoch 

Modification of the Martian cratered highlands continued in the Late Noachian by volcanic, sedimentary, and 

impact processes, although at overall reduced rates and extents 

(*, Golombek and others, 2006; Tanaka and others, 2014). 

These processes resulted in the accumulation of deposits 

in both inter- and intra-crater basins, mapped herein as the 

Late Noachian highland unit (lNh). Unit lNh includes ejecta 

associated with three impact craters that are >150 km across: 

Becquerel and Green craters and Orcus Patera (table 4). Unit 

lNh occurs mostly near unit eNh outcrops, as well as along the 

eastern margins of Thaumasia Planum and Tempe Terra. They 

also occur locally in Middle Noachian-dominated Arabia Terra, 

northern Terra Sabaea, other areas along the highland/lowland transition zone, and the annulus of Argyre Planitia. These 

associations suggest that areas of higher relief experienced 

enhanced precipitation and erosion, resulting in sedimentation 

in adjacent topographic depressions (including impact craters) 

near the end of the Noachian Period (*, Howard and others, 

2005; Irwin and others, 2005; Mest and Crown, 2006; Fassett 

and Head, 2008a,b; Grant and others, 2009; Hynek and others, 

2010). In some cases, outflow channels such as Mawrth and 

Ma’adim Valles were carved by large water discharges resulting 

from overtopping of highland basins or breakouts from overpressured aquifers (*, Carr, 1979; Irwin and others, 2004; Irwin 

and Grant, 2009). 

Denudation is indicated along the margins of Thaumasia 

Planum and Tempe Terra by local terraces, which are interpreted 

to be eroded strata and mapped as unit Nhu. The deposition 

of the resulting detritus may have contributed to outcrops of 

unit lNh. Within Argyre and Hellas Planitiae, basin floors are 

occupied by the Noachian and Hesperian basin unit (HNb), 

suggesting infilling by sedimentation and perhaps volcanism 

(*, Leonard and Tanaka, 2001; Moore and Wilhelms, 2001, 

2007; Hiesinger and Head, 2002). Also, the northeastern margin 

of Hellas basin includes an outcrop of unit lNh resulting from 

fluvial sedimentation and volcanism that has been dissected 

and modified by later fluvial activity and other processes 

(Bleamaster and Crown, 2010).

The layered Hesperian and Noachian highland undivided 

unit (HNhu) in Meridiani Planum has been directly (though 

locally) observed by the Opportunity Mars Exploration Rover 

(*, Squyres and others, 2006). Previous work indicates a Late 

Noachian to Hesperian age for this outcrop (Hynek and Phillips, 

2008), and large craters within and buried by the unit indicate 

a Middle Noachian age for the underlying surface (that of unit 

mNh) (locality 24 in table 2). This deposit of unit HNhu is 

composed of sulfate-rich eolian and fluvial material covered by 

a hematite-rich erosional lag (*, Grotzinger and others, 2005) 

and may result primarily from aeolian deposition followed by 

groundwater alteration (*, Andrews-Hanna and others, 2007), 

as well as by fluvial and marine processes (*, Dohm and others, 

2009a). 

The oldest recognizable volcanic flows and plainsforming deposits on Mars are mapped as the Late Noachian 

volcanic unit (unit lNv), which occurs in the Tharsis region 

and Hellas basin. The most extensive outcrop of unit lNv

forms a furrowed deposit in Malea Planum that appears to 

be sourced from circular paterae displaying low rims and 

depressed centers (*, Leonard and Tanaka, 2001; Plescia, 2004; 

Williams and others, 2009). The two most distinctive paterae 

in this region, Amphitrites and Peneus Paterae, are mapped as 

the Noachian volcanic edifice unit (Nve). Tyrrhenus Mons, 

northeast of Hellas basin (also mapped as unit Nve), exhibits 

highly dissected flanks surrounding a central caldera complex 

and provides evidence for prolonged volcanic activity beginning with explosive volcanism emplacing pyroclastic flows in 

the Late Noachian (*, Greeley and Crown, 1990; Gregg and 

others, 1998). Apollinaris Mons (units Nve and Hve) occurs 

along the highland-lowland transition zone and reveals a long 

history of volcanic, hydrologic, and perhaps hydrothermal 

activity (*, El Maarry and others, 2012). Several irregularly 

shaped, unmapped depressions tens of kilometers across of 

Late Noachian to Early Hesperian age along the transition zone 

in northern Arabia Terra have been proposed to be volcanic 

calderas (Michalski and Bleacher, 2013). Outcrops of unit lNv

that contain lava-flow lobes occur in Thaumasia Planum, as 

well as in scattered plains south of Daedalia Planum. Some 

outcrops of unit lNh north of Olympus Mons (deformed by 

Acheron Fossae), in southwestern Tempe Terra, and in parts of 

the Thaumasia highlands may be volcanic given their proximity to the Tharsis region, but swarms of grabens and other 

modificational features may have obscured potential volcanic 

morphologies. 

Late Noachian crustal deformation is confirmed where 

tectonic structures transect Late Noachian surfaces that are 

partly buried by Early Hesperian outcrops. These include (1) 

dense swarms of narrow grabens of Claritas Fossae and in Icaria 

Planum radial to Syria Planum, likely in response to lithospheric flexure due to loading by the Tharsis rise (*, Banerdt 

and others, 1992; Tanaka and Davis, 1988; Anderson and 

others, 2001); (2) generally west-northwest-trending grabens of 

Acheron Fossae (Kronberg and others, 2007); and (3) grabens 

within and resulting from uplift of the Thaumasia highlands 

(*, Dohm and others, 2001a). Although Late Noachian surfaces 

are commonly deformed by wrinkle ridges, the cumulative 

amount of deformation is comparable to that on Early Hesperian 

surfaces, suggesting that contractional deformation was minor 

in the Late Noachian. The Valles Marineris troughs began to 

form during this epoch by rifting, as indicated by crosscutting 

and stratigraphic relations among rock materials and tectonic 

structures, particularly along the western margin of Thaumasia 

Planum (Witbeck and others, 1991; Dohm and others, 2001a, 

2009b). Most of these structures relate to development of the 

Tharsis rise, indicating that this immense feature had become 

the dominant magmatic and tectonic locus for the planet by the 
12

end of the Noachian (*, Tanaka and others, 1991; Anderson and 

others, 2001).

Hesperian Period

The Hesperian represents an intermediate period of Mars’ 

evolutionary chronology that generally preserves much more 

diverse processes than the Noachian, due to less cumulative 

impact gardening and reduced mean erosion rates (*, Hartmann 

and Neukum, 2001; Golombek and others, 2006). Hesperian 

activity was dominated by extensive volcanism, tectonism, 

chaos and outflow channel development; northern plains and 

polar accumulations; and mass wasting and deposition along 

the highland/lowland transition zone. Generally, resurfacing of the Martian cratered highlands was more localized 

during the Hesperian Period, which included at least four large 

impacts 150 to 200 km in diameter (Gale, Holden, Lowell, and 

Bakhuysen). Acidic weathering conditions during the Hesperian 

led to sulfate enrichment of layered deposits in Valles Marineris 

and Gale crater (Hesperian transition undivided unit, Htu) and 

in Schiaparelli, Terby, and other highland craters (Hesperian 

and Noachian highland undivided unit, HNhu) (*, Bibring 

and others, 2006). Tharsis-related volcanism and catastrophic 

outflow flooding were major contributors to resurfacing during 

the Hesperian Period at local to possibly global scales (*, Hynek 

and others, 2003; Baker and others, 2007; Dohm and others, 

2009a). The overall amount of formation of precipitation-fed 

runoff valleys and sedimentary deposits was reduced relative to 

that of the Noachian, leading to just a few local highland examples (*, Grant and Schultz, 1990; Mest and Crown, 2002, 2003; 

Mangold and others, 2008). Nine occurrences of the Hesperian 

volcanic edifice unit (Hve) are mapped in the Tharsis, Elysium, 

and northeast Hellas basin regions, and the southern fan deposit 

of Apollinaris Mons also is mapped as unit Hve (the remainder 

of the volcano is made up of unit Nve). Although construction 

of Martian volcanic edifices appears to be dominated by effusive volcanism, evidence for pyroclastic volcanism is apparent 

at Apollinaris Mons and Hadriacus Mons and in the Elysium 

region (*, Tanaka and others, 1992: Crown and Greeley, 1993, 

2007; El Maarry and others, 2012).

Some of the most pronounced erosion of geologic terrains 

on Mars took place during the Hesperian. Along the highland/

lowland transition zone, complex arrays of remnant Noachian 

highland-material inliers are surrounded by Hesperian plainsforming mass-wasting deposits (*, Tanaka and others, 2005), 

including the Hesperian and Noachian transition unit (HNt). 

Troughs of Valles Marineris and depressions east and northeast of Valles Marineris were the sites of extensive collapse 

and flood discharges that resulted in (1) the modification of 

Noachian highland units to form “chaotic terrain” (Sharp, 

1973), mapped herein as the Hesperian transition unit (Ht), and 

(2) the carving of and sedimentation within outflow channels 

(forming the Hesperian transition outflow unit, Hto) (*, Rotto 

and Tanaka, 1995; Tanaka, 1997; Chapman and others, 2010). 

The eastern rim of Hellas basin presents another area of outflow 

channel erosion (Crown and others, 1992, 2005; Tanaka and 

Leonard, 1995). In the highland/lowland transition zone south 

of the Elysium rise, layered, wind-carved deposits (units Htu

and AHtu) may be pyroclastic or other eolian fines (identified as the Medusae Fossae Formation; Scott and Tanaka, 

1982, 1986; Hynek and others, 2003; Mandt and others, 2008), 

perhaps sourced locally (Scott and Tanaka, 1982) from Tharsis 

volcanoes (Hynek and others, 2003) or from Apollinaris Mons 

(Kerber and others, 2011)). Locally, unit Htu includes possible aqueous deposits (DiBiase and others, 2013). Watters and 

others (2007) noted that units Htu and AHtu generally have 

a low radar dielectric constant, consistent with either highly 

porous sediment or ice-rich material covered with thin lags. 

Consistent with our age assignments, Kerber and Head (2010) 

and Zimbelman and Scheidt (2012) both found that a large proportion of these units (although they mapped them differently) 

were originally formed in the Hesperian. 

The oldest mapped outcrops of ice-rich polar deposits 

span the Hesperian Period. The plains-forming Hesperian polar 

unit (Hp) and edifice-forming Hesperian polar edifice unit 

(Hpe) surround Planum Australe and may have been emplaced 

through cryovolcanic eruption (Tanaka and Kolb, 2001) and 

(or) from accumulation of a glacial ice sheet (Head and Pratt, 

2001). Unit Hp is marked by narrow sinuous ridges that represent either inverted fluvial channels or eskers (*, Head and 

Pratt, 2001; Tanaka and Kolb, 2001; Ghatan and Head, 2004). 

Additional polar mounds and depressions of unit Hpe form 

Scandia Tholi and Scandia Cavi near Planum Boreum and may 

result from mud volcanism and diapirism (Tanaka and others, 

2003, 2011; Skinner and Mazzini, 2009). The basal materials of 

Planum Boreum comprise a thickly layered mixture of ice and 

dust (Phillips and others, 2008; Putzig and others, 2009; Tanaka 

and Fortezzo, 2012) mapped as the Hesperian polar undivided 

unit (Hpu).

Early Hesperian Epoch

The Early Hesperian volcanic unit (eHv) identifies areally extensive lava fields that partly bury the margins and 

high-standing internal surfaces of the Tharsis rise, as well 

as Hesperia and Syrtis Major Plana (*, Hiesinger and Head, 

2004). The Spirit Mars Exploration Rover demonstrated that 

the Gusev crater floor is covered by lavas that date to this time 

(*, Squyres and others, 2004; Greeley and others, 2005). The 

Early Hesperian highland unit (eHh) is likely made up of a variety of plains-forming rocks and sediments of uncertain origin. 

Components may include volcanic rocks proximal to major 

volcanic centers and perhaps interbedded eolian and lacustrine 

sediments throughout inter-crater highland basins, some that 

show dissection, including inlet and outlet valleys (*, Grant 

and Schultz, 1990; Cabrol and Grin, 1999; Goudge and others, 

2012). Four unit HNt outcrops close to one another in Terra 

Sirenum and Terra Cimmeria include dense clusters of degraded 

mesas and knobs. Plains with scattered knobs mapped as the 

Early Hesperian transition unit (eHt) occur along the highland/

lowland boundary and east of Elysium rise, apparently resulting 

from mass-wasting and other resurfacing processes (*, Tanaka 

and others, 2003). Some of the knobs may be juvenile volcanic 

or mud vents (Skinner and Tanaka, 2007), although the presence 
13

of buried crater and trough forms in the unit suggests it is dominated by unconsolidated sediments rather than by volcanic rock. 

In eastern Hellas Planitia, the Early Hesperian basin unit (eHb) 

may have been emplaced and modified by eolian, lacustrine, 

and (or) volcanic processes (*, Tanaka and Leonard, 1995; 

Moore and Wilhelms, 2001, 2007; Crown and others, 2005; 

Bleamaster and Crown, 2010). 

Tectonism during the Early Hesperian was dominated over 

most of Mars by widespread crustal contraction, perhaps related 

to planetary cooling, which formed arrays of moderate- to highrelief wrinkle ridges in most unit outcrops of this age (units 

eHh, eHv, eHt, and eHb) (*, Tanaka and others, 1991; Watters, 

1993). Wrinkle ridges vary in orientation and commonly follow 

buried circular impact structures (*, Watters, 1993). The chasmata of Valles Marineris continued to form during the Early 

Hesperian (Witbeck and others, 1991) as a result of at least 

limited crustal extension, perhaps along steeply dipping faults 

(Andrews-Hanna, 2012). Crustal extension, related to increased 

regional magmatism, resulted in the formation of graben arrays 

in volcanic rocks (unit eHv) within and marginal to the Tharsis 

rise (*, Anderson and others, 2001). Some Early Hesperian 

rocks are dissected by fluvial channels, including those in 

southwestern Hesperia Planum, suggesting persistent, volcanically driven groundwater discharge toward Hellas Planitia in 

the Hesperian (*, Squyres and others, 1987; Crown and others, 

1992, 2005; Tanaka and Leonard, 1995; Price, 1998).

Late Hesperian Epoch

The Late Hesperian volcanic unit (lHv) covers several 

areas of the Tharsis region and a small area that extends 

southwest from Tyrrhenus Mons (Greeley and Crown, 1990); 

Syria and Solis Plana and Noctis Fossae are the most areally 

extensive. Unit lHv appears to be dominated by lava flows, 

and two internal contacts demarcate sub-regions of contrasting relative ages, as determined by overlap relations and flow 

trends. The Late Hesperian volcanic field unit (lHvf) includes 

many small shields and fissure vents around Syria Planum. Unit 

lHvf also occurs in central and northeastern parts of the Tharsis 

region and on the western flank of Elysium Mons (*, Tanaka 

and others, 1992; Moore, 2001; Hauber and others, 2011). The 

Amazonian and Hesperian volcanic unit (AHv) includes most 

lava-flow surfaces that generally slope away from Tharsis, Alba, 

and Elysium Montes. Although individual flow surface ages are 

highly variable (*, Platz and Michael, 2011), we note that Late 

Hesperian flows are common in this unit, except in close proximity to the Tharsis Montes, where the flows are Amazonian 

in age (Scott and Tanaka, 1981b, 1986). Unit lHvf has been 

modified by extensional tectonism during the Late Hesperian, 

resulting in narrow grabens oriented both radial and concentric 

to shield structures, as well as to the elliptical crest of Syria 

Planum (*, Anderson and others, 2001, 2004).

The Late Hesperian transition unit (lHt) covers many 

lower-elevation, plains-forming parts of the highland-lowland 

transition zone, as well as the floor and some flank areas of 

Valles Marineris and a knobby plain southeast of Hesperia 

Planum. This unit consists of materials emplaced from erosion, 

re-deposition, and mass-wasting of material from adjacent, 

higher-standing highland outcrops (Witbeck and others, 1991; 

Tanaka and others, 2003, 2005). The Amazonian and Hesperian 

transition undivided unit (AHtu) forms the later of the two 

transition undivided units, which may have been emplaced 

beginning in the Late Hesperian. This later unit appears to have 

accumulated after a hiatus, evidenced by inverted fluvial landforms (*, Burr and others, 2009), wrinkle ridges, and a denser 

impact crater population on the surface of unit Htu. Unit AHtu

may be largely reworked from unit Htu and from itself on a 

continuous or episodic basis (Kerber and others, 2011). We also 

include in this unit an outcrop located west of Kasei Valles, surrounded by and stratigraphically within unit AHv, that is pitted 

and possibly layered as evidenced by changes in pit size with 

levels in the exposure.

Unit lHt and parts of unit lHv contain wrinkle ridges, 

although these have less relief than adjacent, Early Hesperian 

surfaces, indicating continuing global contraction after the Early 

Hesperian but with lower cumulative strain. Dendritic valleys 

locally occur on unit lHt around Echus Chasma, documenting 

precipitation-driven overland flow (Mangold and others, 2008). 

Other evidence for fluvial erosion in the Late Hesperian is 

sparse.

The termination of the Late Hesperian Epoch is identified herein as the broad-scale cessation of the emplacement of 

sedimentary plains in the northern lowlands as represented by 

the Late Hesperian lowlands unit, lHl (Tanaka, 1986; Parker 

and others, 1989; Tanaka and others, 2003, 2005; Werner and 

others, 2011). This unit was likely emplaced (and subsequently 

modified) through a variety of geologic processes and may 

form complexly intercalated deposits, perhaps dominated by 

highland debris transported via outflow channels into Chryse 

Planitia and the lowlands beyond (*, Parker and others, 1989; 

Baker and others, 1991; Kreslavsky and Head, 2002; Fairén and 

others, 2003; Buczkowski and Cooke, 2004; Dohm and others, 

2009a). Other contributing processes may include mass wasting 

and fluvial dissection of the highland-lowland transition zone 

(*, Frey and others, 1988; Maxwell and McGill, 1988; Tanaka 

and others, 2001, 2003), volcanism, and eolian erosion and 

deposition. The lHl unit includes scattered, heavily modified 

materials forming low-relief and perhaps thinly buried knobs 

and mesas, some of which may pre-date the Late Hesperian. 

Unit lHl embays unit lHt and other older units, indicating 

distinct temporal separation. The Late Hesperian basin unit 

(lHb) makes up most of Hellas Planitia and may have resulted 

from a combination of volcanic, lacustrine, glacial, and eolian 

deposition (Kargel and Strom, 1992; Tanaka and Leonard, 1995; 

Moore and Wilhelms, 2001, 2007).

Amazonian Period

Although the Amazonian may be the longest geologic 

period for Mars (table 1), a cold, dry, and oxidizing environment (Bibring and others, 2006), reduced global impact flux 

(Hartmann and Neukum, 2001), and sporadic—though perhaps 

more regionally concentrated and episodic—volcanism and 

fluvial/glacial activity (*, Dohm and others, 2008; Neukum 
14

and others, 2010; Grant and Wilson, 2011) suggest that rates of 

material deposition and cumulative amounts of geologic modification in comparison with previous epochs were significantly 

reduced (Golombek and others, 2006; Tanaka and others, 2014). 

Accumulation of polar layered deposits and dunes (*, Kolb and 

Tanaka, 2001; Koutnik and others, 2002), mid-latitude ice-cored 

lobate debris aprons (*, Pierce and Crown, 2003; Chuang and 

Crown, 2005; Plaut and others, 2009), and possible lower-latitude relict mountain glacial moraines likely relate to obliquitydriven effects on the climate during various episodes within 

the Amazonian (*, Laskar and others, 2002; Head and others, 

2003). Magmatic-driven processes may have also contributed to 

environmental change (*, Dohm and others, 2008). 

The history of polar ice and sediment accumulations is 

best documented for the Late Amazonian. The Amazonian polar 

unit (Ap) makes up Cavi Angusti (adjacent to Planum Australe) 

and is poorly dated due to modification by pits and coalesced 

depressions that may have resulted from removal of ice by 

sublimation and cryovolcanism or volcanic activity (Tanaka and 

Kolb, 2001; Ghatan and others, 2003).

The Amazonian volcanic edifice unit (Ave) consists of the 

largest shield volcanoes in the Tharsis region—Olympus, Alba, 

Ascraeus, Pavonis, and Arsia Montes. The ages of the materials 

buried within these edifices are unknown and may be Hesperian 

or earlier in age, given that surrounding lava plains of the 

Tharsis rise date back at least to the Late Noachian (unit lNv). 

Volcanism during this period accounts for a large portion of 

unit AHv that surrounds Tharsis, Elysium, and Alba Montes. In 

contrast, the periphery of Olympus Mons includes several lobes 

of a rugged, ridged terrain mapped here as the Amazonian apron 

unit (Aa). These deposits, also known as the Olympus Mons 

“aureole deposits” (*, Morris, 1982; Morris and Tanaka, 1994), 

are interpreted to have formed by gravity-spreading of outer 

parts of the volcano’s shield (*, McGovern and Morgan, 2009). 

Unit Aa also includes landslides and slumps in Valles Marineris, 

which likely formed throughout the Amazonian (Quantin and 

others, 2004). The Amazonian and Hesperian transition unit 

(AHtu) continued to accumulate during the Amazonian, perhaps 

through volcanic air-fall deposition and eolian reworking 

(*, Scott and Tanaka, 1982; Hynek and others, 2003; Mandt and 

others, 2008; Kerber and others, 2011). 

Early Amazonian Epoch 

Galle and Lyot impact basins, each ~220 km in diameter 

and mapped as unit AHi, formed during this epoch. Hummocky 

flows compose the Amazonian volcanic unit (Av) in two settings. 

Northwest of Elysium Mons, unit Av flows are dissected by 

channels and extend >1,400 km from the margin of the Elysium 

rise into Utopia basin and are interpreted to be volcanically 

induced debris flows (lahars) that emanated from the rise and 

subsequently were modified by fluvial activity (*, Christiansen, 

1989; Tanaka and others, 1992; Russell and Head, 2003). The 

Av unit located northwest of Olympus Mons is likely Early 

to Middle Amazonian lava flows (Tanaka and others, 2005), 

which appear to originate from beneath the Amazonian apron 

unit (Aa) and extend 2,000 km from the edifice. Average slopes 

are only 0.01° for the Olympus Mons outcrop and 0.05° for the 

Elysium rise and Utopia basin flows. The latter largely grade 

into the hummocky, flat Early Amazonian basin unit (eAb) that 

fills the lowest part of Utopia Planitia. The unit also occurs as a 

single outcrop in the low-elevation part of Hellas Planitia, which 

displays layering and reticulate ridge patterns at high resolution 

and may be the result of deposition in ice-covered lakes and of 

subsequent deformation (Moore and Wilhelms, 2001, 2007).

Modest tectonism during the Early Amazonian occurred in 

areas where volcanism and sedimentation appear to have contributed to local crustal loading. Northeast of Alba Mons, northernmost extensions of densely arrayed narrow grabens dissect 

the Late Hesperian lowland unit (lHl); the overall fault system 

that deforms Alba Mons may have resulted from regional rifting 

due to northwest-southeast extension and local, hotspot-induced 

buoyant doming of the Alba Mons shield (*, Tanaka, 1990; 

Cailleau and others, 2005). In addition, gravitational shear 

stresses resulting from the immense shield may have caused it 

to spread northward toward the lowlands, prior to building of 

the summit edifice (Ivanov and Head, 2006). Northwest of Alba 

Mons, wrinkle ridges oriented circumferential to the edifice 

may have formed in response to lithospheric loading imposed 

by growth of the shield and by overall loading of the Tharsis 

rise (*, Banerdt and others, 1992; Watters, 1993; Head and 

others, 2002). Wrinkle ridges associated with Utopia and Isidis 

Planitiae similarly may have resulted from loading by emplacement of volcanic, lowland, and basin units, including units AHv, 

Av, lHl, eAb, and possibly earlier transition units; deformation 

may have begun in the Hesperian (or Noachian) and continued 

into the Early Amazonian (Thomson and Head, 2001; Head and 

others, 2002; Tanaka and others, 2003, 2005).

Middle Amazonian Epoch 

This epoch features emplacement of the Middle 

Amazonian lowland unit (mAl), based on superposition relations and crater counts (Werner and others, 2011; Skinner and 

others, 2012). This unit formerly covered much of the northern 

lowlands, but the majority of the unit appears to have been 

removed (Skinner and others, 2012), accounting for extensive 

remnant crater-topped mounds and mesas of the unit commonly 

referred to as “pedestal craters” (*, Kadish and others, 2010). 

The unit may be mostly dust and ice derived from erosion of 

the Hesperian polar undivided unit (Hpu); subsequent, gradual 

erosion of unit mAl led to pedestal crater formation and perhaps 

re-deposition as the Amazonian polar undivided unit (Apu) 

(Skinner and others, 2012). 

Elsewhere, Middle Amazonian geologic activity included 

(1) continued but reduced volcanism in the Tharsis and Elysium 

regions (contributing to units AHv and Av) (Hauber and others, 

2011; Platz and Michael, 2011) and perhaps in the highlandlowland transition zone (unit AHtu) (*, Hynek and others, 

2003) and (2) apron unit (Aa) development at Olympus Mons 

and Valles Marineris and along the highland-lowland transition 

(unit ANa). Evidence for Middle Amazonian tectonism is sparse 

(*, Anderson and others, 2001).
15

Late Amazonian Epoch

This epoch includes substantial coverage of low-lying parts 

of Amazonis Planitia by sparsely cratered lava flows sourced 

southwest of Olympus Mons and flow fields south and east of 

the Elysium rise that erupted from Cerberus Fossae (*, Fuller 

and Head, 2002; Plescia, 2003; Tanaka and others, 2005; 

Dohm and others, 2008; Vaucher and others, 2009; Hamilton 

and others, 2010; Hauber and others, 2011; Platz and Michael, 

2011). Part of the Cerberus Fossae flows reach into Amazonis 

and Arcadia Planitiae, where they overlie older volcanic flows 

as well as transitional and lowland units. These outcrops, as 

well as other flows surrounding the base of Olympus Mons and 

south of Alba Mons, are mapped as the Late Amazonian volcanic unit (lAv). In Elysium Planitia, unit lAv includes a branch 

that extends northward along the eastern margin of Elysium 

Mons (Hamilton and others, 2010; Hamilton, 2013). The Late 

Amazonian volcanic field unit (lAvf) is composed of groups 

of small basaltic shields, fissure vents, and emanating lava 

flows; the unit occurs in central parts of the Tharsis rise and at 

Cerberus Fossae, commonly along graben swarms (*, Bleacher 

and others, 2007; Vaucher and others, 2009; Hauber and others, 

2011). Formation of narrow grabens and wrinkle ridges during 

the Late Amazonian is limited to volcanic regions and generally 

follows older deformation patterns.

The Amazonian polar undivided unit (Apu) was emplaced 

on the polar plateaus, Planum Boreum and Planum Australe, 

during the Late Amazonian (Tanaka and Kolb, 2001; Koutnik 

and others, 2002; Tanaka, 2005; Tanaka and others, 2008; 

Tanaka and Fortezzo, 2012). These deposits are overlain by 

residual ices, forming the Late Amazonian polar cap unit 

(lApc). The south polar ice cap is colder than the north polar 

ice cap due to its higher elevation and includes carbon dioxide 

ice overlying water ice (*, Byrne, 2009), as well as a buried, 

pitted radar-transparent material as much as 300 m thick that is 

interpreted to be carbon dioxide ice (Phillips and others, 2011). 

Planum Boreum is surrounded by the most extensive accumulations of dune sands on Mars, mapped as the Late Amazonian 

polar dune unit (lApd) (Tanaka and Fortezzo, 2012); unmapped, 

smaller patches of dunes occur globally (*, Hayward and others, 

2007). The Late Amazonian apron unit (lAa) occurs along 

the western to northwestern flanks of the Tharsis Montes and 

Olympus Mons and was mapped in greater detail by Morris 

and Tanaka (1994), Scott and Zimbelman (1995), and Scott and 

others (1998). This unit is dominated by ribbed, lobate aprons 

that are interpreted as drop moraines produced by cold-based 

glaciers (*, Head and others, 2003).

Major Results

Several advancements in the characterization and analysis of 

Martian geology have resulted from this global mapping effort, in 

part determined by additional studies (see cited references):

1. This map is based mainly on improved topographic and 

image data not available in the previous global mapping 

effort, enabling much more consistent observation of 

critical morphologic details and stratigraphic relations 

that have resulted in a very different and more refined 

map (compare tables 6 and 7). Highland materials make 

up 44 percent of the surface, volcanic materials 22 percent, and other basin, transition, lowland, polar, apron, 

and impact materials make up the remaining 34 percent 

(Tanaka and others, 2014).

2. Compilation of stratigraphic relations and crater-density 

statistics for map units on a global scale have resulted 

in the most accurate planet-wide dating of Martian 

geologic materials yet achieved (see also Platz and 

others, 2013). A revised list of referent map units has 

been selected to define each of the eight Martian epochs 

(table 1). For the first time on a geologic map of Mars, 

chronostratigraphic ages are incorporated in unit names.

3. The surface of Mars is appreciably older overall than 

previously understood. The Noachian makes up 45 

percent of the surface, the Hesperian 29 percent, and the 

Amazonian 26 percent. (For more details on the character and resurfacing rates of Mars through time, see 

Tanaka and others, 2014). 

4. The Early, Middle, and Late Noachian highland units 

(eNh, mNh, and lNh, respectively) have statistically 

distinct ages, and the units occur at progressively lower 

mean elevations with successively younger age. Crater 

morphology statistics indicate that Noachian resurfacing was spatially non-uniform, long-lived, and gravity 

driven, which is consistent with volcanism and arid-zone 

fluvial and aeolian erosion (Irwin and others, 2013).

5. All impact basins >150 km in diameter have been dated 

and show a dramatically reduced rate of formation over 

time: >65 for Early Noachian, >15 for Middle Noachian, 

~3 for Late Noachian, ~4 for Hesperian, and 2 for Early 

Amazonian (table 4).

Acknowledgments

Stuart Robbins (University of Colorado, Boulder) generously supplied us with his global digital crater database of 

Mars (Robbins and Hynek, 2012) prior to its publication. We 

are indebted to Mike Carr, David Crown, Ernst Hauber, Brian 

Hynek, Scott Mest, Mike Shand, Mike Smith, and David 

Williams for constructive reviews. We also benefited from 

discussions, conference presentations, and publications of 

many other researchers referenced herein. Most of this work 

was supported by NASA’s Planetary Geology and Geophysics 

Program. Work by Platz was funded by the Helmholtz 

Association through the research alliance “Planetary Evolution 

and Life” and a German Research Foundation (Deutsche 

Forschungsgemeinschaft) grant (PL613/1), and efforts by 
16

Michael by the German Space Agency (Deutsches Zentrum 

für Luft- und Raumfahrt, Bonn), grant 50QM1001 (High 

Resolution Stereo Camera on Mars Express), on behalf of the 

German Federal Ministry of Economics and Technology.

References Cited

Acuña, M.H., Connerney, J.E.P., Wasilewski, R.P., and 

11 others, 2001, Magnetic field of Mars—Summary 

of results from the aerobraking and mapping orbits: 

Journal of Geophysical Research, v. 106, no. E10, p. 

23,404–23,417.

Anderson, R.C., Dohm, J.M., Golombek, M.P., and 5 others, 

2001, Significant centers of tectonic activity through 

time for the western hemisphere of Mars: Journal of 

Geophysical Research, v. 106, p. 20,563–20,585.

Anderson, R.C., Dohm, J.M., Haldemann, A.F.C., Hare, T.M., 

Baker, V.R., 2004, Tectonic histories between Alba Patera 

and Syria Planum, Mars: Icarus, v. 171, p. 31–38. 

Anderson, R.S., and Anderson, S.P., 2010, Geomorphology—

The mechanics and chemistry of landscapes: New York, 

Cambridge University Press, 654 p.

Andrews-Hanna, J.C., 2012, The formation of Valles 

Marineris—1. Tectonic architecture and the relative roles of extension and subsidence: Journal 

of Geophysical Research, v. 117, no. E03006 

(doi:10.1029/2011JE003953).

Andrews-Hanna, J.C., Phillips, R.J., and Zuber, M.T., 2007, 

Meridiani Planum and the global hydrology of Mars: 

Nature, v. 446, p. 163–166 (doi:10.1038/nature05594).

Andrews-Hanna, J.C., Zuber, M.T., and Banerdt, B., 2008, 

The Borealis basin and the origin of the Martian crustal 

dichotomy: Nature, v. 453, p. 1212–1215 (doi:10.1038/

nature07011).

Baker, V.R., Carr, M.H., Gulick, V.C., Williams, C.R., and 

Marley, M.S., 1992, Channels and valley networks, in 

Kieffer, H.H., Jakosky, B.M., Snyder, C.W., and Matthews, 

M.S., eds., Mars: Tucson, University of Arizona Press, p. 

493–522. 

Baker, V.R., Maruyama, Shigenori, Dohm, J.M., 2007, Tharsis 

superplume and the geological evolution of early Mars, 

in Yuen, D.A., Maruyama, Shigenori, Karato, S.-I., and 

Windley, B.F., eds., Superplumes—Beyond plate tectonics: 

Dordrecht, Springer, p. 507–523.

Baker, V.R., Strom, R.G., Gulick, V.C., and 3 others, 1991, 

Ancient oceans, ice sheets, and the hydrological cycle on 

Mars: Nature, v. 352, p. 589–594.

Bandfield, J.L., Hamilton, V.E., and Christensen, P.R., 2000, A 

global view of Martian surface compositions from MGSTES: Science, v. 287, p. 1626–1630.

Banerdt, W.B., Golombek, M.P., and Tanaka, K.L., 1992, Stress 

and tectonics on Mars, in Kieffer, H.H., Jakosky, B.M., 

Snyder, C.W., and Matthews, M.S., eds., Mars: Tucson, 

Ariz., University of Arizona Press, P. 249–297.

Banks, M.E., Byrne, Shane, Galla, Kapil, and 6 others, 2010, 

Crater population and resurfacing of the Martian north 

polar layered deposits: Journal of Geophysical Research, v. 

115, no. E08006 (doi:10.1029/2009JE003523).

Barlow, N.G., 2008, Mars—An introduction to its interior, surface, and atmosphere: Cambridge, Cambridge University 

Press, 264 p.

Batson, R.M., Bridges, P. M., and Inge, J.L., 1979, Atlas of 

Mars, the 1:5,000,000 map series: National Aeronautics 

and Space Administration Special Publication 438, 146 p.

Bell, J.F., ed., 2008, The Martian surface—Composition, mineralogy, and physical properties: Cambridge, Cambridge 

University Press, 636 p.

Bibring, J.-P., Langevin, Yves, Gendrin, Aline, and 37 

others, 2005, Mars surface diversity as revealed by the 

OMEGA/Mars Express observations: Science, v. 307, p. 

1576–1581.

Bibring, J.-P., Langevin, Yves, Mustard, J.F., and 40 others, 

2006, Global mineralogical and aqueous Mars history 

derived from OMEGA/Mars Express data: Science, v. 312, 

p. 400–404.

Bleacher, J.E., Greeley, Ronald, Williams, D.A., and 2 others, 

2007, Trends in effusive style at the Tharsis Montes, Mars, 

and implications for the development of the Tharsis province: Journal of Geophysical Research, v. 112, no. E09005 

(doi:10.1029/2006JE002873).

Bleamaster, L.F., and Crown, D.A., 2010, Geologic map of 

MTM –40277, –45277, –40272, and –45272 quadrangles, 

eastern Hellas Planitia regions of Mars: U.S. Geological 

Survey Scientific Investigations Map 3096, scale 

1:1,000,000.

Bouysee, Philippe, 2009, Geological map of the world at 

1:50,000,000 (3rd ed.): Paris, France, Commission for the 

Geological Map of the World, scale 1:50,000,000, two 

sheets and explanatory notes.

Buczkowski, D.L., and Cooke, M.L., 2004, Formation of 

double-ring circular grabens due to volumetric compaction over buried impact craters—Implications for thickness and nature of cover material in Utopia Planitia, Mars: 

Journal of Geophysical Research, v. 109, no. E02006 

(doi:10.1029/2003JE002144).

Burr, D.B., Nega, M.-T., Williams, R.M.E., and 3 others, 

2009, Pervasive aqueous paleoflow features in the Aeolis/

Zephyria Plana region, Mars: Icarus, v. 200, p. 52–76 

(doi:10.1016/j.icarus.2008.10.014).

Byrne, Shane, 2009, The polar deposits of Mars: Annual 

Reviews of Earth and Planetary Science, v. 37, p. 535–560.

Cabrol, N.A., and Grin, E.A., 1999, Distribution, classification, 

and ages of Martian impact crater lakes: Icarus, v. 142, p. 

160–172.

Cailleau, Béatrice, Walter, T.R., Janle, Peter, and Hauber, Ernst, 

2005, Unveiling the origin of radial grabens on Alba Patera 

volcano by finite element modeling: Icarus, v. 176, p. 

44–56 (doi:10.1016/j.icarus.2005.01.017).

Carr, M.H., 1979, Formation of Martian flood features by 

release of water from confined aquifers: Journal of 

Geophysical Research, v. 84, p. 2995–3007.

Chapman, M.G., Neukum, Gerhard, Dumke, Alexander, and 

8 others, 2010, Noachian-Hesperian geologic history of 
17

the Echus Chasma and Kasei Valles system on Mars—

New data and interpretations: Earth and Planetary 

Science Letters, v. 294, p. 256–271 (doi:10.1016/j.

epsl.2009.11.032).

Christensen, P.R., Jakosky, B.M., Kieffer, H.H., and 8 others, 

2004, The Thermal Emission Imaging System (THEMIS) 

for the Mars 2001 Odyssey mission: Space Science 

Reviews, v. 110, p. 85–130.

Christiansen, E.H., 1989, Lahars in the Elysium region of Mars, 

Geology, v. 17, p. 203–206.

Chuang, F.C., and Crown, D.A., 2005, Surface characteristics 

and degradational history of debris aprons in the Tempe 

Terra/Mareotis Fossae region of Mars: Icarus, v. 179, p. 

24–42 (doi:10.1016/j.icarus.2005.05.014).

Chuang, F.C., and Crown, D.A., 2009, Geologic map of MTM 

35337, 40337, and 45337 quadrangles, Deuteronilus 

Mensae region of Mars: U.S. Geological Survey Scientific 

Investigations Map 3079, scale 1:1,000,000.

Connerney, J.E.P., Acuña, M.H., Wasilewski, P.J., and 5 others, 

2001, The global magnetic field of Mars and implications 

for crustal evolution: Geophysical Research Letters, v. 28, 

no. 21, p. 4015–4018.

Craddock, R.A., and Howard, A.D., 2002, The case for rainfall on 

a warm, wet early Mars: Journal of Geophysical Research, 

v., 107, no. E11, 5111 (doi:10.1029/2001JE001505).

Crown, D.A., Bleamaster, L.F., III, and Mest, S.C., 2005, Styles 

and timing of volatile-driven activity in the eastern Hellas 

region of Mars: Journal of Geophysical Research, v. 110, 

no. E12S22 (doi:10.1029/2005JE002496).

Crown, D.A., and Greeley, Ronald, 1993, Volcanic geology of Hadriaca Patera and the eastern Hellas region 

of Mars: Journal of Geophysical Research, v. 98, p. 

3431–3451.

Crown, D.A., and Greeley, Ronald, 2007, Geologic map 

of MTM –30262 and –30267 quadrangles, Hadriaca 

Patera region of Mars: U.S. Geological Survey Scientific 

Investigations Map 2936, scale 1:1,004,000.

Crown, D.A., Price, K.H., and Greeley, Ronald, 1992, Geologic 

evolution of the east rim of the Hellas basin, Mars: Icarus, 

v. 100, p. 1–25.

Crumpler, L.S., Craddock, R.A., and Aubele, J.C., 2001, 

Geologic map of the MTM 25047 and 20047 quadrangles, 

central Chryse Planitia/Viking 1 Lander site, Mars: U.S. 

Geological Survey Geologic Investigations Series Map 

I–2693, scale 1:1,000,000.

Crumpler, L.S., Head, J.W., and Aubele, J.C., 1996, Calderas 

on Mars—Characteristics, structure, and associated 

flank deformation: Geological Society, London, Special 

Publications, January 1, 1996, v. 110, p. 307–348 

(doi:10.1144/GSL.SP.1996.110.01.24).

Davila, A.F., Fairén, A.G., Stokes, C.R., and 5 others, 2013, 

Evidence for Hesperian glaciation along the Martian 

dichotomy boundary: Geology, v. 41, no. 7, p. 755–758 

(doi:10.1130/G34201.1).

Des Marais, D.J., 2010, Exploring Mars for evidence of habitable environments and life: Proceedings of the American 

Philosophical Society, v. 154, no. 4, p. 402–421.

DiAchille, Gaetano, and Hynek, B.M., 2010, Ancient ocean on 

Mars supported by global distribution of deltas and valleys: Nature Geoscience, v. 3, p. 459–463 (doi:10.1038/

ngeo891).

DiBiase, R.A., Limaye, A.B., Scheingross, J.S., Fischer, W.W., 

and Lamb, M.P., 2013, Deltaic deposits at Aeolis Dorsa—

Sedimentary evidence for a standing body of water on 

the northern plains of Mars: Journal of Geophysical 

Research, Planets, v. 118, p. 1285–1302 (doi:10.1002/

jgre.20100).

Dickson, J.L., Head, J.W., and Marchant, D.R., 2008, Late 

Amazonian glaciation at the dichotomy boundary on 

Mars—Evidence for glacial thickness and multiple 

glacial phases: Geology, v. 36, 411–414 (doi:10.1130/

G24382A.1).

Dohm, J.M., Anderson, R.C., Barlow, N.G., and 19 others, 

2008, Recent geological and hydrological activity on 

Mars—The Tharsis/Elysium corridor: Planetary and 

Space Science, v. 56, no. 7, p. 985–1013 (doi:10.1016/j.

pss.2008.01.001).

Dohm, J.M., Baker, V.R., Boynton, W.V., and 18 others, 

2009a, GRS evidence and the possibility of ancient 

oceans on Mars: Planetary and Space Science, v. 57, p. 

664–684.

Dohm, J.M., Ferris, J.C., Baker, V.R., and 7 others, 2001b, 

Ancient drainage basin of the Tharsis region, Mars—

Potential source for outflow channel systems and putative 

oceans or paleolakes: Journal of Geophysical Research, v. 

106, p. 32,943–32,958.

Dohm, J.M., Miyamoto, Hirdy, Maruyama, Shigenori, and 11 

others, 2013, Mars evolution, in A.G. Fairén, ed., Mars—

Evolution, geology, and exploration: Hauppauge, NY, 

Nova Science Publishers, Inc., p. 1–34.

Dohm, J.M., Tanaka, K.L., and Hare, T.M., 2001a, Geologic, 

paleotectonic, and paleoerosional maps of the Thaumasia 

region, Mars: U.S. Geological Survey Geologic 

Investigations Series Map I–2650, scale 1:5,000,000.

Dohm, J.M., Williams, J.-P., Anderson, R.C., and 13 others, 

2009b, New evidence for a magmatic influence on the 

origin of Valles Marineris, Mars: Journal of Volcanology 

and Geothermal Research, v. 185, p. 12–27.

Edwards, C.S., Nowicki, K.J., Christensen, P.R., and 3 

others, 2011, Mosaicking of global planetary image 

datasets—1. Techniques and data processing for Thermal 

Emission Imaging System (THEMIS) multi-spectral data: 

Journal of Geophysical Research, v. 116, no. E10008 

(doi:10.1029/2010JE003755).

Ehlmann, B.L., Mustard, J.F., Murchie, S.L., and 11 others, 

2008, Orbital identification of carbonate-bearing rocks on 

Mars: Science, v. 322, p. 1828–1832.

Ehlmann, B.L., Mustard, J.F., Murchie, S.L., and 4 others, 

2011, Subsurface water and clay mineral formation 

during the early history of Mars: Nature, v. 479, p. 53–60 

(doi:10.1038/nature10582).

Ehlmann, B.L., Mustard, J.F., Swayze, G.A., and 9 others, 

2009, Identification of hydrated silicate minerals on 

Mars using MRO-CRISM—Geologic context near 
18

Nili Fossae and implications for aqueous alteration: 

Journal of Geophysical Research, v. 114, no. E00D08 

(doi:10.1029/2009JE003339).

El Maarry, M.R., Dohm, J.M., Marzo, G.A., and 5 others, 

2012, Searching for evidence of hydrothermal activity 

at Apollinaris Mons, Mars: Icarus, v. 217, p. 297–314 

(doi:10.1016/j.icarus.2011.10.022).

Fairén, A.G., Davila, A.F., Gago-Duport, L., Haqq-Misra, J.D., 

Gil, C., McKay, C.P., and Kasting, J.F., 2011, Cold glacial 

oceans would have inhibited phyllosilicate sedimentation 

on early Mars: Nature Geoscience, v. 4667–4670.

Fairén, A.G., Dohm, J.M., Baker, V.R., de Pablo, M.A., Ruiz, J., 

Ferris, J.C., and Anderson, R.C., 2003, Episodic flood inundations of the northern plains of Mars: Icarus, v. 165, p. 53–67.

Fassett, C.I., and Head, J.W., III, 2008a, The timing of Martian 

valley network activity—Constraints from buffered 

crater counting: Icarus, v. 195, p. 61–89 (doi:10.1016/j.

icarus.2007.12.009).

Fassett, C.I., and Head, J.W., III, , 2008b, Valley network-fed, 

open-basin lakes on Mars—Distribution and implications 

for Noachian surface and subsurface hydrology: Icarus, v. 

198, p. 37–56 (doi:10.1016/j.icarus.2008.06.016).

Federal Geographic Data Committee [prepared for the Federal 

Geographic Data Committee by the U.S. Geological 

Survey], 2006, FGDC Digital Cartographic Standard 

to Geologic Map Symbolization: Reston, Va., Federal 

Geographic Data Committee Document Number FGDCSTD–013–2006, 290 p., 2 plates.

Fergason, R.L., Christensen, P.R., and Kieffer, H.H., 

2006, High resolution thermal inertia derived 

from THEMIS—Thermal model and applications: 

Journal of Geophysical Research, v. 111, no. E12004 

(doi:10.1029/2006JE002735).

Frey, H.V., 2006, Impact constraints on, and a chronology for, major events in early Mars history: Journal 

of Geophysical Research, v. 111, no. E08S91 

(doi:10.1029/2005JE002449).

Frey, H.V., Roark, J.H., Shockey, K.M., Frey, E.L., and 

Sakimoto, S.E.H., 2002, Ancient lowlands on Mars: 

Geophysical Research Letters, v. 29, no. 10, 1384, 

(doi:10.1029/2001GL013832).

Frey, H.V., Semeniuk, A.M., Semeniuk, J.A., and Tokarcik, 

Susan, 1988. A widespread common age resurfacing 

event in the highland-lowland transition zone in eastern 

Mars: Proceedings of the Lunar and Planetary Science 

Conference, 18th, p. 679–699.

Fuller, R.R., and Head, J.W., III, 2002, Amazonis Planitia—The 

role of geologically recent volcanism and sedimentation 

in the formation of the smoothest plains on Mars: Journal 

of Geophysical Research, v. 107, no. E10, p. 11–1—11–25 

(doc. no. 5081, doi:10.1029/2002JE001842).

Ghatan, G.J., and Head, J.W., III, 2004, Regional drainage of 

meltwater beneath a Hesperian-aged south circumpolar ice 

sheet on Mars: Journal of Geophysical Research, v. 109, 

no. E07006 (doi:10.1029/2003JE002196).

Ghatan, G.J., Head, J.W., III, and Pratt, Stephen, 2003, Cavi 

Angusti, Mars—Characterization and assessment of 

possible formation mechanisms: Journal of Geophysical 

Research, v. 108, no. E5, p. 11–1 to 11–19 (doc. no. 5045, 

doi:10.1029/2002JE001972).

Golombek, M.P., Anderson, F.S., and Zuber, M.T., 2001, 

Martian wrinkle ridge topography—Evidence for subsurface faults from MOLA: Journal of Geophysical 

Research, v. 106, no. E10, p. 23,811–23,821 

(doi:10.1029/2000JE001308).

Golombek, M.P., Cook, R.A., Economou, Thanasis, and 11 

others, 1997, Overview of the Mars Pathfinder mission and 

assessment of landing site predictions: Science, v. 278, p. 

1743–1748.

Golombek, M.P., Grant, J.A., Crumpler, L.S., and 8 others, 

2006, Erosion rates at the Mars Exploration Rover 

landing sites and long-term climate change on Mars: 

Journal of Geophysical Research, v. 111, no. E12S10 

(doi:10.1029/2006JE002754).

Goudge, T.A., Head, J.W., Mustard, J.F., and Fassett, C.I., 

2012, An analysis of open-basin lake deposits on Mars—

Evidence for the nature of associated lacustrine deposits 

and post-lacustrine modification processes: Icarus, v. 219, 

p. 211–229 (doi:10.1016/j.icarus.2012.02.027).

Grant, J.A., and Schultz, P.H., 1990, Gradational epochs on 

Mars—Evidence from west-northwest of Isidis Basin and 

Electris: Icarus, v. 84, p. 166–195.

Grant, J.A., and Wilson, S.A., 2011, Late alluvial fan 

formation in southern Margaritifer Terra, Mars: 

Geophysical Research Letters, v. 38, no. L08201 

(doi:10.1029/2011GL046844).

Grant, J.A., Wilson, S.A., Fortezzo, C.M., and Clark, D.A., 

2009, Geologic map of MTM –20012 and –25012 quadrangles, Margaritifer Terra region of Mars: U.S. Geological 

Survey Scientific Investigations Map 3041, scale 

1:1,000,000.

Greeley, Ronald, and Crown, D.A., 1990, Volcanic geology of 

Tyrrhena Patera, Mars: Journal of Geophysical Research, v. 

95, p. 7133–7149.

Greeley, Ronald, Foing, B.H., McSween, H.Y., Jr., and 6 

others, 2005, Fluid lava flows in Gusev crater, Mars: 

Journal of Geophysical Research, v. 110, no. E05008 

(doi:10.1029/2005JE002401).

Greeley, Ronald, and Guest, J.E., 1987, Geologic map of the 

eastern equatorial region of Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–1802–B, scale 

1:15,000,000.

Gregg, T.K.P., Crown, D.A., and Greeley, Ronald, 1998, 

Geologic map of MTM quadrangle –20252, Tyrrhena 

Patera region of Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–2556, scale 

1:500,000.

Grosfils, E.B., and Head, J.W., 1994, The global distribution of 

giant radiating dike swarms on Venus—Implications for 

the global stress state: Geophysical Research Letters, v. 21, 

p. 701–704.

Grotzinger, J.P., Arvidson, R.E., Bell, J.F., III, and 17 others, 

2005, Stratigraphy and sedimentology of a dry to wet 

eolian depositional system, Burns formation, Meridiani 
19

Planum, Mars: Earth and Planetary Science Letters, v. 240, 

p. 11–72 (doi:10.1016/j.epsl.2005.09.039).

Hamilton, C.W., 2013, Flood lavas associated with the Cerberus 

Fossae 2 unit in Elysium Planitia, Mars [abs.], in Lunar 

and Planetary Science Conference LXXV, Abstract #3070 

[CD-ROM; online].

Hamilton, C.W., Fagents, S.A., and Wilson, Lionel, 2010, 

Explosive lava-water interactions in Elysium Planitia, 

Mars—Constraints on the formation of the Tartarus Colles 

cone groups: Journal of Geophysical Research, v.115, no. 

E9 (doi:10.1029/2009JE003546).

Hansen, V.L., 2000, Geologic mapping of tectonic planets: 

Earth and Planetary Science Letters, v. 176, p. 527–542.

Hartmann, W.K., 2005, Martian cratering 8—Isochron refinement and the chronology of Mars: Icarus, v. 174, p. 

294–320 (doi:10.1016/j.icarus.2004.11.023).

Hartmann, W.K., and Neukum, Gerhard, 2001, Cratering chronology and the evolution of Mars: Space Science Reviews, 

v. 96, p. 165–194.

Hauber, Ernst, Brož, Petr, Jagert, Felix, Jodłowski, Piotr, and 

Platz, Thomas, 2011. Very recent and wide-spread basaltic 

volcanism on Mars: Geophysical Research Letters, v. 38, 

no. L10201 (doi:10.1029/2011GL047310).

Hauber, Ernst, Grott, Matthias, and Kronberg, Peter, 2010, 

Martian rifts—Structural geology and geophysics: 

Earth and Planetary Science Letters, v. 294, p. 393–410 

(doi:10.1016/j.epsl.2009.11.005).

Hayward, R.K., Mullins, K.F., Fenton, L.K., and 5 others, 

2007, Mars global digital dune database and initial science results: Journal of Geophysical Research, v. 112, no. 

E11007 (doi:10.1029/2007JE002943).

Head, J.W., III, Kreslavsky, M.A., and Pratt, Stephen, 2002, 

Northern lowlands of Mars—Evidence for widespread volcanic flooding and tectonic deformation in the Hesperian 

Period: Journal of Geophysical Research, v. 107, no. E1, 

5004 (10.1029/2000JE001445).

Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., and 

Marchant, D.R., 2003, Recent ice ages on Mars: Nature, v. 

426, p. 797–802.

Head, J.W., III, and Pratt, Stephen, 2001, Extensive Hesperianaged south polar ice sheet on Mars—Evidence for massive 

melting and retreat, and lateral flow and ponding of meltwater: Journal of Geophysical Research, v. 106, no. E6, p. 

12,275–12,299.

Hiesinger, Harald, and Head, J.W., III, 2000, Characteristics 

and origin of the polygonal terrain in southern Utopia 

Planitia, Mars—Results from Mars Orbiter Laser Altimeter 

and Mars Orbiter Camera data: Journal of Geophysical 

Research, v. 105, p. 11,999–12,022.

Hiesinger, Harald, and Head, J.W., III, 2002, Topography and 

morphology of the Argyre Basin, Mars—Implications for 

its geologic and hydrologic history: Planetary and Space 

Science, v. 50, p. 929–981.

Hiesinger, Harald, and Head, J.W., III, 2004, The Syrtis Major 

volcanic province, Mars—Synthesis from Mars Global 

Surveyor data: Journal of Geophysical Research, v. 109, 

no. E01004 (doi:10.1029/2003JE002143).

Hodges, C.A., and Moore, H.J., 1994, Atlas of volcanic landforms on Mars: U.S. Geological Survey Professional Paper 

1534, 194 p.

Hoke, M.R.T., and Hynek, B.M., 2009, Roaming zones of precipitation on ancient Mars as recorded in valley networks: 

Journal of Geophysical Research, v. 114, no. E08002 

(doi:10.1029/2008JE003247).

Howard, A.D., 1978, Origin of the stepped topography of the 

Martian poles: Icarus, v. 34, p. 581–599.

Howard, A.D., 2000, The role of eolian processes in forming 

surface features of the Martian polar layered deposits: 

Icarus, v. 144, p. 267–288.

Howard, A.D., Moore, J.M., and Irwin, R.P., III, 2005, An 

intense terminal epoch of widespread fluvial activity on 

early Mars—1. Valley network incision and associated 

deposits: Journal of Geophysical Research, v. 110, no. 

E12S14 (doi:10.1029/2005JE002459).

Hynek, B.M., Beach, Michael, and Hoke, M.R.T., 2010, 

Updated global map of Martian valley networks and 

implications for climate and hydrologic processes: 

Journal of Geophysical Research, v. 115, no. E09008 

(doi:10.1029/2009JE003548). 

Hynek, B.M., and Phillips, R.J., 2008, The stratigraphy of 

Meridiani Planum, Mars, and implications for the layered 

deposits’ origin: Earth and Planetary Science Letters, v. 

274, p. 214–220 (doi:10.1016/j.epsl.2008.07.025).

Hynek, B.M., Phillips, R.J., and Arvidson, R.E., 2003, 

Explosive volcanism in the Tharsis region—Global 

evidence in the Martian geologic record: Journal of 

Geophysical Research, v. 111, no. E9 (doc no. 5111, 

doi:10.1029/2003JE002062).

Irwin, R.P., III, and Grant, J.A., 2009, Large basin overflow 

floods on Mars, in Burr, D.M., Carling, P.A., and Baker, 

V.R., eds., Megaflooding on Earth and Mars: Cambridge, 

UK, Cambridge University Press, p. 209–224.

Irwin, R.P., III, and Grant, J.A., 2013, Geologic map of MTM 

–15027, –20027, –25027, and –25032 quadrangles, 

Margaritifer Terra region of Mars: U.S. Geological Survey 

Science Investigations Map 3209, scale 1:1,000,000.

Irwin, R.P., III, Howard, A.D., Craddock, R.A., and Moore, 

J.M., 2005, An intense terminal epoch of widespread 

fluvial activity on early Mars—2. Increased runoff and 

paleolake development: Journal of Geophysical Research, 

v. 110, no. E12S15 (doi:10.1029/2005JE002460).

Irwin, R.P., III, Howard, A.D., and Maxwell, T.A., 2004, 

Geomorphology of Ma’adim Vallis, Mars, and associated 

paleolake basins: Journal of Geophysical Research, v. 109, 

no. E12009 (doi:10.1029/2004JE002287).

Irwin, R.P., III, Tanaka, K.L., and Robbins, S.J., 2013, 

Distribution of Early, Middle, and Late Noachian cratered surfaces in the Martian highlands—Implications for 

resurfacing events and processes: Journal of Geophysical 

Research, v. 118, 1–14 (doi:10.1002/jgre.20053).

Ivanov, B.A., 2001, Mars/Moon cratering rate ratio estimates: 

Space Science Reviews, v. 96, p. 87–104.

Ivanov, M.A., and Head, J.W., 2006, Alba Patera, Mars—

Topography, structure, and evolution of a unique 
20

late Hesperian–early Amazonian shield volcano: 

Journal of Geophysical Research, v. 111, no. E09003 

(doi:10.1029/2005JE002469).

Kadish, S.J., Head, J.W., and Barlow, N.G., 2010, Pedestal 

crater heights on Mars—A proxy for the thicknesses 

of past, ice-rich, Amazonian deposits: Icarus, v. 210, p. 

92–101 (doi:10.1016/j.icarus.2010.06.021).

Kargel, J.S., and Strom, R.G., 1992, Ancient glaciation on Mars: 

Geology, v. 20, p. 3–7.

Kerber, Laura, and Head, J.W., 2010, The age of the Medusae 

Fossae Formation—Evidence of Hesperian emplacement from crater morphology, stratigraphy, and ancient 

lava contacts: Icarus, v. 206, p. 669–684 (doi:10.1016/j.

icarus.2009.10.001).

Kerber, Laura, Head, J.W., Madeleine, J.-B., Forget, François, 

and Wilson, Lionel, 2011, The dispersal of pyroclasts from 

Apollinaris Patera, Mars—Implications for the origin of 

the Medusae Fossae Formation: Icarus, v. 216, p. 212–220 

(doi:10.1016/j.icarus.2011.07.035).

Klein, H.P., Horowitz, N.H., and Biemann, Klaus, 1992: 

The search for extant life on Mars, in Kieffer, H.H., 

Jakosky, B.M., Snyder, C.W., and Matthews, M.S., 

eds., Mars: Tucson, University of Arizona Press, p. 

1221–1245.

Kneissl, Thomas, van Gasselt, Stephan, and Neukum, Gerhard, 

2011, Map-projection-independent crater size-frequency 

determination in GIS environments—New software tool 

for ArcGIS: Planetary and Space Science, v. 59, p. 1243–

1254 (doi:10.1016/j.pss.2010.03.015).

Kolb, E.J., and Tanaka, K.L., 2001, Geologic history of the 

polar regions of Mars based on Mars Global Surveyor 

data—II. Amazonian Period: Icarus, v. 154, p. 22–39.

Kopparapu, R.K., Ramirez, Ramses, Kasting, J.F., and 7 others, 

2013, Habitable zones around main-sequence stars—New 

estimates: The Astrophysics Journal, v. 265, no. 2, 131 

(doi:10.1088/0004-637X/765/2/131).

Koutnik, M.R., Byrne, Shane, and Murray, B.C., 2002, South 

polar layered deposits of Mars—The cratering record: 

Journal of Geophysical Research, v. 107, no. E11, p. 

5100–5112.

Kreslavsky, M.A., and Head, J.W., III, 2000, Kilometer-scale 

roughness of Mars—Results from MOLA data analysis: Journal of Geophysical Research, v. 105, no. E11, p. 

26,695–26,711.

Kreslavsky, M.A., and Head, J.W., III, 2002, Fate of outflow 

channel effluents in the northern lowlands of Mars—The 

Vastitas Borealis Formation as a sublimation residue from 

frozen ponded bodies of water: Journal of Geophysical 

Research, v. 107, no. E12, p. 4–1 to 4–25 (doc. no. 5121, 

doi:10.1029/2001JE001831).

Kronberg, Peter, Hauber, Ernst, Grott, Matthias, and 6 others, 

2007, Acheron Fossae, Mars—Tectonic rifting, volcanism, and implications for lithospheric thickness: 

Journal of Geophysical Research, v. 112, no. E04005 

(doi:10.1029/2006JE002780).

Langevin, Ives, Poulet, François, Bibring, J.–P., and Gondet, 

Brigitte, 2005, Sulfates in the north polar region of Mars 

detected by OMEGA/Mars Express: Science, v. 307, p. 

1584–1586.

Langlais, B., Purucker, M.E., and Mandea, Mioara, 2004, Crustal 

magnetic field of Mars: Journal of Geophysical Research, v. 

109, no. E02008 (doi:10.1029/2003JE002048).

Laskar, Jacques, Correia, A.C.M., Gastineau, Mickaël, and 3 

others, 2004, Long term evolution and chaotic diffusion of 

the insolation quantities of Mars: Icarus, v. 170, p. 343–

364 (doi:10.1016/j.icarus.2004.04.005). 

Laskar, Jacques, Levrard, Benjamin, and Mustard, J.F., 2002, 

Orbital forcing of the martian polar layered deposits: 

Nature, v. 419, p. 375–377.

Lemoine, F.G., Smith, D.E., Rowlands, D.D., and 4 others, 

2001. An improved solution of the gravity field of Mars 

(GMM–2B) from Mars Global Surveyor: Journal of 

Geophysical Research, v. 106, no. E10, p. 23,359–23,376.

Leonard, G.J., and Tanaka, K.L., 2001, Geologic map of the 

Hellas region of Mars: U.S. Geological Survey Geologic 

Investigations Series Map I–2694, scale 1:5,000,000.

Leverington, D.W., 2011, A volcanic origin for the outflow 

channels of Mars: Key evidence and major implications: Geomorphology, v. 132, p. 51–75 (doi:10.1016/j.

geomorph.2011.05.022).

Lucchitta, B.K., 1982, Ice sculpture in the Martian outflow 

channels: Journal of Geophysical Research, v. 87, no. B12, 

p. 9951–9973.

Malin, M.C., Bell, J.F., III, Cantor, B.A., and 11 others, 

2007, Context Camera investigation on board the Mars 

Reconnaissance Orbiter: Journal of Geophysical Research, 

v. 112, no. E5 (doi:10.1029/2006JE002808).

Mandt, K.E., de Silva, S.L., Zimbelman, J.R., and 

Crown, D.A., 2008, Origin of the Medusae Fossae 

Formation, Mars: Insights from a synoptic approach: 

Journal of Geophysical Research, v. 113, no. E12011 

(doi:10.1029/2008JE003076).

Mangold, Nicolas, Ansan, Véronique, Masson, Phillipe, 

and 2 others, 2008, Geomorphic study of fluvial landforms on the northern Valles Marineris plateau, Mars: 

Journal of Geophysical Research, v. 113, no. E08009 

(doi:10.1029/2007JE002985).

Maxwell, T.A., and McGill, G.E., 1988, Ages of fracturing and 

resurfacing in the Amenthes region, Mars: Proceeding of the 

Lunar and Planetary Science Conference, 18th, p. 701–711.

McGill, G.E., 1989, Buried topography of Utopia, Mars: 

Persistence of a giant impact depression: Journal of 

Geophysical Research, v. 94, p. 2753–2759.

McGill, G.E., 2002, Geologic map transecting the highland/lowland 

boundary zone, Arabia Terra, Mars—Quadrangles 30332, 

35332, 40332, and 45332: U.S. Geological Survey Geologic 

Investigations Series Map I–2746, scale 1:1,000,000.

McGill, G.E., 2005, Geologic map of Cydonia Mensae–

southern Acidalia Planitia, Mars—Quadrangles MTM 

40007, 40012, 40017, 45007, 45012, and 45017: U.S. 

Geological Survey Geologic Investigations Series Map 

I–2811, scale 1:1,000,000.

McGovern, P.J., and Morgan, J.K., 2009, Volcanic spreading 

and lateral variations in the structure of Olympus Mons, 
21

Mars: Geology, v. 37, no. 2, p. 139–142 (doi:10.1130/

G25180A.1).

Mest, S.C., and Crown, D.A., 2002, Geologic map of MTM 

–40252 and –40257 quadrangles, Reull Vallis region of 

Mars: U.S. Geological Survey Geologic Investigations 

Series Map I–2730, scale 1:1,000,000.

Mest, S.C., and Crown, D.A., 2003, Geologic map of MTM 

–45252 and –45257 quadrangles, Reull Vallis region of 

Mars: U.S. Geological Survey Geologic Investigations 

Series Map I–2763, scale 1:1,000,000.

Mest, S.C., and Crown, D.A., 2006, Geologic map of MTM 

–20272 and –25272 quadrangles, Tyrrhena Terra region 

of Mars: U.S. Geological Survey Scientific Investigations 

Map 2934, scale 1:1,004,000.

Michael, G.G., 2013, Planetary surface dating from crater size–

frequency distribution measurements—Multiple resurfacing episodes and differential isochron fitting: Icarus, v. 

226, p. 885–890 (doi:10.1016/j.icarus.2013.07.004).

Michael, G.G., and Neukum, Gerhard, 2010, Planetary surface 

dating from crater size–frequency distribution measurements—Partial resurfacing events and statistical age 

uncertainty: Earth and Planetary Science Letters, v. 294, p. 

223–229 (doi:10.1016/j.epsl.2009.12.041).

Michael, G.G., Platz, Thomas, Kneissl, Thomas, and 

Schmedemann, Nico, 2012, Planetary surface dating from 

crater size frequency distribution measurements: Spatial 

randomness and clustering: Icarus, v. 218, p. 169–177 

(doi:10.1016/j.icarus.2011.11.033).

Michalski, J.R., and Bleacher, J.E., 2013, Supervolcanoes 

within an ancient volcanic province in Arabia Terra, Mars: 

Nature, v. 502, p. 47–52 (doi:10.1038/nature12482).

Moore, H.J., 2001, Geologic map of the Tempe Mareotis region 

of Mars: U.S. Geological Survey Geologic Investigations 

Series Map I–2727, scale 1:1,000,000.

Moore, J.M., and Wilhelms, D.E., 2001, Hellas as a possible 

site of ancient ice-covered lakes on Mars: Icarus, v. 154, p. 

258–276 (doi:10.1006/icar.2001.6736).

Moore, J.M., and Wilhelms, D.E., 2007, Geologic map of part 

of western Hellas Planitia, Mars: U.S. Geological Survey 

Scientific Investigations Map 2953, scale 1:1,004,000.

Morris, E.C., 1982, Aureole deposits of the Martian volcano 

Olympus Mons: Journal of Geophysical Research, v. 87, 

no. B2, p. 1164–1178.

Morris, E.C., and Tanaka, K.L., 1994, Geologic maps of the 

Olympus Mons region of Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–2327, scales 

1:2,000,000 and 1:1,000,000.

Murchie, S.L., Mustard, J.F., Ehlmann, B.L., and 14 others, 

2009, A synthesis of Martian aqueous mineralogy after 1 

Mars year of observations from the Mars Reconnaissance 

Orbiter: Journal of Geophysical Research, v. 114, no. 

E00D06 (doi:10.1029/2009JE003342).

Mustard, J.F., Cooper, C.D., and Rifkin, M.K., 2001, Evidence 

for recent climate change on Mars from the identification of 

youthful near-surface ground ice: Nature, v. 412, p. 411–414.

Neukum, Gerhard, Basilevsky, A.T., Kneissl, Thomas, and 6 

others, 2010, The geologic evolution of Mars—Episodicity 

of resurfacing events and ages from cratering analysis 

of image data and correlation with radiometric ages of 

Martian meteorites: Earth and Planetary Science Letters, v. 

294, p. 204–222 (doi:10.1016/j.epsl.2009.09.006).

Neumann, G.A., Smith, D.E., and Zuber, M.T., 2003. Two 

Mars years of clouds detected by the Mars Orbiter Laser 

Altimeter: Journal of Geophysical Research, v. 108, no. 

E4, 5023 (doi:10.1029/2002JE001849).

Nimmo, Francis, and Tanaka, K.L., 2005, Early crustal evolution of Mars: Annual Review of Earth and Planetary 

Sciences, v. 33, p. 133–161.

Nummedal, Dag, and Prior, D.B., 1981, Generation of Martian 

chaos and channels by debris flows: Icarus, v. 45, p. 77–86.

Ody, Anouck, Poulet, François, Langevin, Yves, and 7 

others, 2012, Global maps of anhydrous minerals 

at the surface of Mars from OMEGA/MEx: Journal 

of Geophysical Research, v. 117, no. E00J14 (doi: 

10.1029/2012JE004117).

Osterloo, M.M., Anderson, F.S., Hamilton, V.E., and Hynek, 

B.M., 2010, Geologic context of proposed chloride-bearing 

materials on Mars: Journal of Geophysical Research, v. 

115, no. E10012, doi:10.1029/2010JE003613.

Parker, T.J., Saunders, R.S., and Schneeberger, D.M., 1989, 

Transitional morphology in west Deuteronilus Mensae, 

Mars—Implications for modification of the lowland/

upland boundary: Icarus, v. 82, p. 111–145.

Phillips, R.J., Davis, B.J., Tanaka, K.L., and 15 others, 2011, 

Massive CO2

 ice deposits sequestered in the south polar 

layered deposits of Mars: Science, v. 332, p. 838–841 

(doi:10.1126/science.1203091).

Phillips, R.J., Zuber, M.T., Smrekar, S.E., and 24 others, 2008, 

Mars north polar deposits—Stratigraphy, age, and geodynamical response: Science, v. 320, p. 1182–1185.

Phillips, R.J., Zuber, M.T., Solomon, S.C., and 8 others, 2001, 

Ancient geodynamics and global-scale hydrology on Mars: 

Science, v. 291, p. 2587–2591, doi:10.1126/science.1058701.

Pierce, T.L., and Crown, D.A., 2003, Morphologic and topographic analyses of debris aprons in the eastern Hellas 

region, Mars: Icarus, v. 163, p. 46– 65 (doi:10.1016/

S0019-1035(03)00046-0).

Platz, Thomas, and Michael, G.G., 2011, Eruption history of 

the Elysium Volcanic Province, Mars: Earth and Planetary 

Science Letters, v. 312, p. 140–151 (doi:10.1016/j.

epsl.2011.10.001).

Platz, Thomas, Michael, G.G., Tanaka, K.L., and 2 others, 2013, 

Crater-based dating of geological units on Mars—Methods 

and application for the new global geological map: Icarus, 

v. 225, p. 806–827 (doi:10.1016/j.icarus.2013.04.021).

Plaut, J.B., Safaeinili, Ali, Holt, J.W., and 5 others, 2009, Radar 

evidence for ice in lobate debris aprons in the mid-northern 

latitudes of Mars: Geophysical Research Letters, v. 36, no. 

L02203 (doi:10.1029/2008GL036379).

Plescia, J.B., 2003, Cerberus Fossae, Elysium, Mars—A source 

for lava and water: Icarus, v. 164, p. 79–95.

Plescia, J.B., 2004, Morphometric properties of Martian volcanoes: Journal of Geophysical Research, v. 109, no. E03003 

(doi:10.1029/2002JE002031).
22

Poulet, François, Bibring, J.–P., Mustard, J.F., and 31 others, 

2005, Phyllosilicates on Mars and implications for early 

martian climate: Nature, v. 438, p. 623–627 (doi:10.1038/

nature04274).

Price, K.H., 1998, Geologic map of the Dao, Harmakhis, and 

Reull Valles region of Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–2557, scale 

1:1,000,000.

Putzig, N.E., and Mellon, M.T., 2007, Apparent thermal inertia 

and the surface heterogeneity of Mars: Icarus, v. 191, p. 

68–94 (doi:10.1016/j.icarus.2007.05.013).

Putzig, N.E., Phillips, R.J., Campbell, B.A., and 7 others, 

2009, Subsurface structure of Planum Boreum from Mars 

Reconnaissance Orbiter Shallow Radar soundings: Icarus, 

v. 204, p. 443–457 (doi:10.1016/j.icarus.2009.07.034).

Quantin, Cathy, Allemand, Pascal, Mangole, Nicolas, 

and Delacourt, Christophe, 2004, Ages of Valles 

Marineris (Mars) landslides and implications 

for canyon history: Icarus, v. 172, p. 555–572 

(doi:10.1016/j.icarus.2004.06.013).

Reed, J.C., Jr., Wheeler, J.O., and Tucholke, B.E., comps., 

2005, Geologic Map of North America: Boulder, Colorado, 

Geological Society of America, Continent–Scale Map–001, 

scale 1:5,000,000.

Robbins, S.J., and Hynek, B.M., 2012, A new global database of 

Mars impact craters ≥1 km—1. Database creation, properties, and parameters: Journal of Geophysical Research, v. 

117, no. E05004 (doi:10.1029/2011JE003966).

Robbins, S.J., Hynek, B.M., Lillis, R.J., and Bottke, W.F., 2013, 

Large impact crater histories of Mars—The effect of different model crater age techniques: Icarus, v. 225, p. 173–184 

(doi:10.1016/j.icarus.2013.03.019).

Rotto, Sue, and Tanaka, K.L., 1995, Geologic/geomorphologic 

map of the Chryse Planitia region of Mars: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–2441, 

scale 1:5,000,000.

Russell, P.S., and Head, J.W., 2003, Elysium-Utopia flows 

as mega-lahars—A model of dike intrusion, cryosphere cracking, and water-sediment release: Journal 

of Geophysical Research, v. 108, no. E6, 5064 

(doi:10.1029/2002JE001995).

Schultz, P.H., Schultz, R.A., and Rogers, John, 1982, Structure 

and evolution of ancient impact basins on Mars: Journal of 

Geophysical Research, v. 87, p. 9803–9820.

Schultz, R.A., Moore, J.M., Grosfils, E.B., Tanaka, K.L., and 

Mège, Daniel, 2007, The Canyonlands model for planetary grabens—Revised physical basis and implications, 

in Chapman, M.G. (ed.), The geology of Mars—Evidence 

from Earth-based analogs: Cambridge, UK Cambridge 

University Press, p. 371–399.

Schultz, R.A., and Tanaka, K.L., 1994, Lithospheric-scale buckling and thrust structures on Mars—The Coprates rise and 

south Tharsis ridge belt: Journal of Geophysical Research, 

v. 99, no. E4, p. 8371–8385.

Scott, D.H., and Carr, M.H., 1978, Geologic map of Mars: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map I–1083, scale 1:25,000,000.

Scott, D.H., Dohm, J.M., and Zimbelman, J.R., 1998, Geologic 

map of Pavonis Mons volcano, Mars: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–2561, 

scale 1:1,000,000.

Scott, D.H., and Tanaka, K.L., 1981a, Mars—A large highland 

volcanic province revealed by Viking images, in Lunar 

and Planetary Science Conference, Proceedings, Houston, 

Texas, March 16–20, 1981, New York: Pergamon Press, v. 

12B, p. 1449–1458. 

Scott, D.H., and Tanaka, K.L., 1981b, Mars—Paleostratigraphic 

restoration of buried surfaces in Tharsis Montes: Icarus, v. 

45, p. 304–319.

Scott, D.H., and Tanaka, K.L., 1982, Ignimbrites of Amazonis 

Planitia region of Mars: Journal of Geophysical Research, 

v. 87, no. B2, p. 1179–1190.

Scott, D.H., and Tanaka, K.L., 1986, Geologic map of the 

western equatorial region of Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–1802–A, scale 

1:15,000,000.

Scott, D.H., and Zimbelman, J.R., 1995, Geologic map of 

Arsia Mons volcano, Mars: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–2480, scale 

1:1,000,000.

Seidelmann, P.K., Abalakin, V.K., Bursa, Michal, and 8 

others, 2002, Report of the IAU/IAG Working Group on 

Cartographic Coordinates and Rotational Elements of the 

Planets and Satellites—2000: Celestial Mechanics and 

Dynamical Astronomy, v. 82, p. 83–110.

Sharp, R.P., 1973, Mars—Fretted and chaotic terrain: Journal of 

Geophysical Research, v. 78, p. 4073–4083.

Skinner, J.A., Jr., and Fortezzo, C.M., 2013, The role of photogeologic mapping in traverse planning—Lessons from 

DRATS 2010 activities: Acta Astronautica, v. 90, no. 2, p. 

242–263 (doi:10.1016/j.actaastro.2011.11.011).

Skinner, J.A., Jr., Hare, T.M., and Tanaka, K.L., 2006. 

Digital renovation of the atlas of Mars 1:15,000,000-

scale global geologic series maps [abs.]: Lunar and 

Planetary Science Conference XXXVII, Abstract 2331 

[CD–ROM; online].

Skinner, J.A., Jr., and Herkenhoff, K.E., 2012, Geologic map 

of the MTM 85200 quadrangle, Olympia Rupēs region of 

Mars: U.S. Geological Survey Science Investigations Map 

3197, scale 1:500,000.

Skinner, J.A., Jr., and Mazzini, Adriano, 2009, Martian mud 

volcanism—Terrestrial analogs and implications for formational scenarios: Marine and Petroleum Geology, v. 26, p. 

1866–1878 (doi:10.1016/j.marpetgeo.2009.02.006).

Skinner, J.A., Jr., and Tanaka, K.L., 2007, Evidence for and 

implications of sedimentary diapirism and mud volcanism in the southern Utopia highland–lowland boundary plain, Mars: Icarus, v. 186, p. 41–59 (doi:10.1016/j.

icarus.2006.08.013).

Skinner, J.A., Jr., Tanaka, K.L., and Platz, Thomas, 2012, 

Widespread loess-like deposit in the Martian northern 

lowlands identifies Middle Amazonian climate change: 

Geology, v. 40, no. 12, p. 1127–1130 (doi:10.1130/

G33513.1).
23

Smith, D.E., Zuber, M.T., Frey, H.V., and 21 others, 2001, 

Mars Orbiter Laser Altimeter—Experiment summary after the first year of global mapping of Mars: 

Journal of Geophysical Research, v. 106, no. E10, p. 

23,689–23,722.

Smith, D.E., Zuber, M.T., Solomon, S.C., and 16 others, 1999, 

The global topography of Mars and implications for surface evolution: Science, v. 284, p. 1495–1503.

Smith, I.B., and Holt, J.W., 2010, Onset and migration of spiral 

troughs on Mars revealed by orbital radar: Nature, v. 465, 

p. 450–453 (doi:10.1038/nature09049).

Smith, M.J, and Pain, C.F., 2009, Applications of remote sensing in geomorphology: Progress in Physical Geography, v. 

33, no. 4, p. 568–582 (doi:10.1177/0309133309346648).

Snyder, C.W., and Moroz, V.I., 1992, Spacecraft exploration of 

Mars, in Kieffer, H.H., Jakosky, B.M., Snyder, C.W., and 

Matthews, M.S., eds., Mars: Tucson, University of Arizona 

Press, p. 71–119.

Squyres, S.W., Arvidson, R.E., Bell, J.F., III, and 47 others, 

2004, The Spirit rover’s Athena science investigation at 

Gusev crater, Mars: Science, v. 304, no. 5685, p. 794–799 

(doi: 10.1126/science.3050794).

Squyres, S.W., Arvidson, R.E., Bollen, Diane, and 51 others, 

2006, Overview of the Opportunity Mars Exploration 

Rover Mission to Meridiani Planum—Eagle Crater to 

Purgatory Ripple: Journal of Geophysical Research, v. 111, 

no. E12S12 (doi:10.1029/2006JE002771).

Squyres, S.W., Wilhelms, D.E., and Moosman, A.C., 1987, 

Large-scale volcano-ground ice interactions on Mars: 

Icarus, v. 70, p. 385–408.

Tanaka, K.L., 1986, The stratigraphy of Mars, in Proceedings of 

the Lunar and Planetary Science Conference, 17th, Part 1, 

November, 1986: Journal of Geophysical Research, v. 91, 

supplement, no. B13, p. E139–158.

Tanaka, K.L., 1990, Tectonic history of the Alba PateraCeraunius Fossae region of Mars: Proceedings of the Lunar 

and Planetary Science Conference, 20th, p. 515–523.

Tanaka, K.L., 1997, Sedimentary history and mass flow structures of Chryse and Acidalia Planitiae, Mars: Journal of 

Geophysical Research, v. 102, no. E2, p. 4131–4149.

Tanaka, K.L., 2005, Geology and insolation-driven climatic history of Amazonian north polar materials on Mars: Nature, 

v. 437, p. 991–994.

Tanaka, K.L., Banerdt, W.B., Kargel, J.S., and Hoffman, Nick, 

2001, Huge, CO2

-charged debris-flow deposit and tectonic 

sagging in the northern plains of Mars: Geology, v. 29, no. 

5, p. 427–430.

Tanaka, K.L., Chapman, M.G., and Scott, D.H., 1992, Geologic 

map of the Elysium region of Mars: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–2147, 

scale 1:5,000,000.

Tanaka, K.L., and Davis, P.A., 1988, Tectonic history of the 

Syria Planum province of Mars: Journal of Geophysical 

Research, v. 93, no. B12, p. 14,893–14,917.

Tanaka, K.L., and Fortezzo, C.M., 2012, Geologic map of 

the north polar region of Mars: U.S. Geological Survey 

Science Investigations Map 3177, scale 1:2,000,000.

Tanaka, K.L., Fortezzo, C.M., Hayward, R.K., and 2 others, 

2011, History of plains resurfacing in the Scandia region 

of Mars: Planetary and Space Science, v. 59, p. 1128–1142 

(doi:10.1016/j.pss.2010.11.004).

Tanaka, K.L., Golombek, M.P., and Banerdt, W.B., 1991, 

Reconciliation of stress and structural histories of the 

Tharsis region of Mars: Journal of Geophysical Research, 

v. 96, no. E1, p. 15,617–15,633.

Tanaka, K.L., Isbell, N.K., Scott, D.H., Greeley, R., and Guest, 

J.E., 1988, The resurfacing history of Mars—A synthesis of digitized, Viking-based geology: Proceedings of 

the Lunar and Planetary Science Conference, 18th, p. 

665–678.

Tanaka, K.L., and Kolb, E.J., 2001, Geologic history of the 

polar regions of Mars based on Mars Global Surveyor 

data—1. Noachian and Hesperian Periods: Icarus, v. 154, 

p. 3–21 (doi:10.1006/icar.2001.6675).

Tanaka, K.L., and Leonard, G.J., 1995, Geology and landscape evolution of the Hellas region of Mars: Journal of 

Geophysical Research, v. 100, no. E3, p. 5407–5432.

Tanaka, K.L., Robbins, S.J., Fortezzo, C.M., Skinner, J.A., Jr., 

and Hare, T.M., 2014, The digital global geologic map 

of Mars—Chronostratigraphic ages, topographic and 

crater morphologic characteristics, and updated resurfacing history: Planetary and Space Science, v. 95, p. 11–24, 

(doi:10.1016/j.pss.2013.03.006).

Tanaka, K.L., Rodriguez, J.A.P., Skinner, J.A., Jr., and 5 others, 

2008, North polar region of Mars—Advances in stratigraphy, structure, and erosional modification: Icarus, v. 196, 

p. 318–358.

Tanaka, K.L., and Scott, D.H., 1987, Geologic map of the polar 

regions of Mars: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1802–C, scale 1:15,000,000.

Tanaka, K.L., Skinner, J.A., Jr., Crumpler, L.S., and Dohm, 

J.M., 2009, Assessment of planetary geologic mapping techniques for Mars using terrestrial analogs—The 

SP Mountain area of the San Francisco Volcanic Field, 

Arizona: Planetary and Space Science, v. 57, p. 510–532 

(doi:10.1016/j.pss.2008.06.012).

Tanaka, K.L., Skinner, J.A., Jr., and Hare, T.M., 2005, 

Geologic map of the northern plains of Mars: U.S. 

Geological Survey Science Investigations Map 2888, scale 

1:15,000,000.

Tanaka, K.L., Skinner, J.A., Jr., and Hare, T.M., 2010, Planetary 

geologic mapping handbook—2010, in Bleamaster, L.F., 

III, Tanaka, K.L., and Kelley, M.S., eds., Abstracts of the 

Annual Meeting of Planetary Geologic Mappers, Flagstaff, 

AZ, 2010: Washington DC, NASA Conference Publication 

CP–2010–217041, appendix, 21 p.

Tanaka, K.L., Skinner, J.A., Jr., Hare, T.M., Joyal, T., and 

Wenker, A., 2003, Resurfacing history of the northern 

plains of Mars based on geologic mapping of Mars Global 

Surveyor data: Journal of Geophysical Research, v. 108, 

no. E4 (doc. no: 8043, doi:10.1029/ 2002JE001908).

Thomson, B.J., and Head, J.W., III, 2001, Utopia Basin, Mars—

Characterization of topography and morphology and 

assessment of the origin and evolution of basin internal 
24

structure: Journal of Geophysical Research, v. 106, no. 

E10, p. 23,209–23,230.

U.S. Geological Survey, 2003, Topographic map of Mars: U.S. 

Geological Survey Geologic Investigations Series Map 

I–2782, scale 1:25,000,000, two sheets.

Varnes, D.J., 1974, The logic of geological maps, with reference 

to their interpretation and use for engineering purposes: 

U.S. Geological Survey Professional Paper 837, 49 p.

Vaucher, Julien, Baratoux, David, Mangold, Nicolas, and 3 

others, 2009, The volcanic history of central Elysium 

Planitia—Implications for Martian magmatism: Icarus, v. 

204, p. 418–442.

Watters, T.R., 1993, Compressional tectonism on Mars: Journal 

of Geophysical Research, v. 98, no. E9, p. 17,049–17,060.

Watters, T.R., Campbell, Bruce, Carter, Lynn, and 10 others, 

2007, Radar sounding of the Medusae Fossae Formation 

Mars—Equatorial ice or dry, low-density deposits?: 

Science, v. 318, p. 1125–1128.

Werner, S.C., 2008, The early martian evolution—Constraints 

from basin formation ages: Icarus, v. 195, p. 45–60 

(doi:10.1016/j.icarus.2007.12.008).

Werner, S.C., 2009, The global martian volcanic evolutionary history: Icarus, v. 201, p. 44–68 (doi:10.1016/j.

icarus.2008.12.019).

Werner, S.C., and Tanaka, K.L., 2011, Redefinition of the 

crater-density and absolute-age boundaries for the chronostratigraphic system of Mars: Icarus, v. 215, p. 603–607, 

(doi:10.1016/j.icarus.2011.07.024).

Werner, S.C., Tanaka, K.L., and Skinner, J.A., Jr., 2011, 

Mars—The evolutionary history of the northern lowlands 

based on crater counting and geologic mapping: Planetary 

and Space Science, v. 59, p. 1143–1165 (doi:10.1016/j.

pss.2011.03.022).

Wilhelms, D.E., 1990, Geologic mapping, in Greeley, Ronald, 

and Batson, R.M., eds., Planetary Mapping: New York, 

Cambridge University Press, p. 208–260.

Williams, D.A., Greeley, Ronald, Ferguson, R.L., and 13 

others (including the HRSC Co-Investigator Team), 

2009, The circum-Hellas volcanic province, Mars—

Overview: Planetary and Space Science, v. 57, p. 895–916 

(doi:10.1016/j.pss.2008.08.010).

Witbeck, N.E., Tanaka, K.L., and Scott, D.H., 1991, Geologic 

map of the Valles Marineris region, Mars: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–2010, 

scale 1:5,000,000.

Wyrick, Danielle, Ferrill, D.A., Morris, A.P., and 2 others, 

2004, Distribution, morphology, and origins of Martian pit 

crater chains: Journal of Geophysical Research, v. 109, no. 

E06005 (doi:10.1029/2004JE002240).

Xiao, Long, Huang, Jun, Christensen, P.R., and 4 others, 2012, 

Ancient volcanism and its implication for thermal evolution of Mars: Earth and Planetary Science Letters, v. 

323–324, p. 9–18 (doi:10.1016/j.epsl.2012.01.027).

Zimbelman, J.R., and Scheidt, S.P., 2012, Hesperian age for 

western Medusae Fossae Formation, Mars: Science, v. 336, 

p. 1683 (doi:10.1126/science.1221094).
25

Epoch Reference crater 

diameter (km)

Cumulative crater 

density (no. > reference diameter 

per 106

 km2)

Start of epoch, Ga Referent 

unit Hartmann 2004 

iteration

Neukum 

system

Late Amazonian 1 160 0.274 0.328 Apu

Middle Amazonian 1 600 1.03 1.23 mAl

Early Amazonian 1 2,100 3.24 3.37 eAb

Late Hesperian 5 125 3.39 3.61 lHl

Early Hesperian 5 200 3.56 3.71 eHv

Late Noachian 16 100 3.85 3.83 lNh

Middle Noachian 16 200 3.96 3.94 mNh

Early Noachian --- --- --- --- eNh

Table 1. Martian epoch lower boundary ages from Michael (2013) based on the Hartmann (2004 iteration in Hartmann, 2005) and Neukum 

(Ivanov, 2001; Hartmann and Neukum, 2001) chronology systems derived from reference crater densities of Tanaka (1986) as updated by 

Werner and Tanaka (2011). Referent units are chosen from this map. ---, no data.
26

(compare to Platz and others, 2013).

Table 2. Assigned model ages1 for selected Mars global map units from 48 representative counting localities2 sorted by latitude from north to south

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

1 lHl 71.10 24.78 69,980

3.51 0.10 0.38 3.61 3.13 lH lH eA3.07 0.16 0.31 3.23 2.76 eA eA eA

2 eHt 49.91 49.50 40,170

3.65 0.04 0.06 3.69 3.59 eH eH lH

3 eAb 47.90 114.00 39,280

3.57 0.07 0.12 3.64 3.45 lH eH lH1.98 0.31 0.31 2.29 1.67 eA eA eA

4 Av 38.06 128.28 13,810

3.52 0.11 0.49 3.63 3.03 lH eH eA0.728 0.095 0.095 0.823 0.633 mA mA mA

5 eAb 37.95 111.20 26,100

3.33 0.11 0.26 3.44 3.07 eA lH eA0.885 0.075 0.075 0.960 0.810 mA mA mA

6 lHl 35.96 330.66 89,930

3.60 0.05 0.08 3.65 3.52 lH eH lH

2.00 0.11 0.11 2.11 1.89 eA eA eA

7 mNh 35.50 47.87 48,850

3.97 0.03 0.03 4.00 3.94 eN eN mN3.57 0.02 0.02 3.59 3.55 lH lH lH

8 lHt 34.91 166.95 23,130

3.71 0.06 0.10 3.77 3.61 eH lN lH3.20 0.14 0.35 3.34 2.85 eA eA eA1.07 0.07 0.07 1.14 1.00 mA mA mA

9 lAv 31.17 193.68 80,780

3.12 0.34 1.70 3.46 1.42 eA lH eA0.072 0.018 0.018 0.090 0.054 lA lA lA

1.00.1

10.5 2 5 

1.00.1

0.5 1 2 5 

15

1.00.1

0.5 1 2 5 

1.00.1

0.5 1 2 5 

29

1.00.1

0.5 1 2 5 

5

1.00.1

0.5 1 2 5 

1

1.00.1

0.5 1 2 5 

21

1.00.1

10.5 2 5 

4

1.00.1

10.5 2 5 

6
27

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

10 lHl 29.75 108.01 30,060

30.27 105.85 3.62 0.05 0.07 3.67 3.55 eH eH lH

1.19 0.08 0.08 1.27 1.11 mA eA mA

11 lHl 26.70 106.38 27,410

3.53 0.07 0.13 3.60 3.40 lH lH lH1.78 0.15 0.15 1.93 1.63 eA eA eA

12 Hto 22.84 316.70 20,360

3.56 0.09 0.21 3.65 3.35 lH eH eA1.20 0.10 0.10 1.30 1.10 mA eA mA

13 lNh 22.70 16.95 9,684

3.78 0.05 0.07 3.83 3.71 lN lN eH3.35 0.06 0.10 3.41 3.25 eA lH eA

14 mNh 22.46 32.20 9,668

3.99 0.03 0.04 4.02 3.95 eN eN eN0.767 0.070 0.070 0.837 0.697 mA mA mA

15 lHt 18.08 117.37 19,190

3.70 0.05 0.07 3.75 3.63 eH lN eH2.01 0.09 0.09 2.10 1.92 eA eA eA

16 eHt 15.92 311.47 31,990

3.72 0.03 0.04 3.75 3.68 lN lN eH2.29 0.11 0.11 2.40 2.18 eA eA eA

17 lHv 14.17 237.52 17,230

3.63 0.07 0.13 3.70 3.50 eH eH lH2.66 0.27 0.31 2.93 2.35 eA eA eA

18 HNt 11.19 161.48 19,700

3.91 0.08 0.18 3.99 3.73 mN eN lN3.77 0.05 0.07 3.82 3.70 lN lN eH1.56 0.12 0.12 1.68 1.44 eA eA eA

Table 2. Assigned model ages1 for selected Mars global map units—Continued

1.00.1

10.5 2 5 

18

1.00.1

10.5 2 5 

3

1.00.1

10.5 2 5 

9

1.00.1

10.5 2 5 

1

1.00.1

10.5 2 5 

21

1.00.1

10.5 2 5 

16

1.00.1

10.5 2 5 

3

1.00.1

10.5 2 5 

12

1.00.1

10.5 2 5 

12
28

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

19 mNh 9.52 51.36 43,600

3.94 0.02 0.03 3.96 3.91 mN eN mN3.69 0.01 0.01 3.70 3.68 eH eH eH

20 mNh 9.43 342.48 22,820

3.91 0.05 0.07 3.96 3.84 mN eN mN3.34 0.04 0.04 3.38 3.30 eA lH eA

21 lAv 5.41 177.26 45,340

3.37 0.18 1.50 3.55 1.87 eA lH eA0.014 0.002 0.002 0.016 0.012 lA lA lA

22 mNh 4.39 16.91 32,160

3.93 0.05 0.08 3.98 3.85 mN eN mN3.68 0.02 0.02 3.70 3.66 eH eH eH

23 mNh 3.98 318.74 26,290

3.89 0.03 0.03 3.92 3.86 mN mN mN3.55 0.02 0.02 3.57 3.53 lH lH lH

24 HNhu 2.76 355.64 11,680

3.91 0.04 0.05 3.95 3.86 mN eN mN2.68 0.33 0.40 3.01 2.28 eA eA eA

25 AHtu 1.16 141.90 8,208

3.46 0.06 0.11 3.52 3.35 lH lH eA

26 Htu 0.51 148.66 20,100

3.70 0.04 0.06 3.74 3.64 eH lN eH1.65 0.15 0.15 1.80 1.50 eA eA eA

27 AHtu -0.01 152.68 57,350

3.50 0.07 0.14 3.57 3.36 lH lH eA

Table 2. Assigned model ages1 for selected Mars global map units—Continued

1.00.1

10.5 2 5 

19

1.00.1

10.5 2 5 

10

1.00.1

10.5 2 5 

6

1.00.1

10.5 2 5 

17

1.00.1

10.5 2 5 

9

1.00.1

10.5 2 5 

17

1.00.1

10.5 2 5 

5

1.00.1

10.5 2 5 

15

1.00.1

10.5 2 5 

1
29

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

28 Htu -4.53 174.64 10,410

3.88 0.08 0.17 3.96 3.71 mN eN lN2.79 0.27 0.35 3.06 2.44 eA eA eA

29 lHv -7.50 252.99 6,508

3.55 0.09 0.28 3.64 3.27 lH eH eA1.59 0.20 0.20 1.79 1.39 eA eA eA

30 AHtu -8.12 182.28 23,890

3.49 0.15 2.10 3.64 1.39 lH eH eA0.231 0.032 0.032 0.263 0.199 lA lA lA

31 mNh -8.50 345.53 21,190

3.87 0.04 0.05 3.91 3.82 mN mN lN3.50 0.03 0.03 3.53 3.47 lH lH lH

32 eNh -14.05 49.41 19,900

3.99 0.04 0.05 4.03 3.94 eN eN mN3.50 0.02 0.03 3.52 3.47 lH lH lH

33 eNh -15.00 82.62 21,530

3.99 0.03 0.04 4.02 3.95 eN eN eN3.50 0.02 0.03 3.52 3.47 lH lH lH

34 lNh -17.74 330.63 39,000

4.08 0.07 0.13 4.15 3.95 eN eN eN3.79 0.02 0.02 3.81 3.77 lN lN lN

35 lNh -21.85 354.96 35,180

3.72 0.06 0.09 3.78 3.63 lN lN eH3.36 0.04 0.06 3.40 3.30 eA lH eA

36 eNh -23.57 35.53 42,060

4.03 0.05 0.07 4.08 3.96 eN eN eN3.82 0.02 0.03 3.84 3.79 lN mN lN3.66 0.01 0.01 3.67 3.65 eH eH eH

Table 2. Assigned model ages1 for selected Mars global map units—Continued

1.00.1

10.5 2 5 

1

1.00.1

10.5 2 5 

46

1.00.1

10.5 2 5 

7

1.00.1

10.5 2 5 

4

1.00.1

10.5 2 5 

27

1.00.1

10.5 2 5 

28

1.00.1

10.5 2 5 

12

1.00.1

10.5 2 5 

4

1.00.1

10.5 2 5 

26
30

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

37 Nhu -27.04 288.95 19,210

3.73 0.02 0.03 3.75 3.70 lN lN eH

38 eHv -28.26 117.58 40,740

3.65 0.04 0.05 3.69 3.60 eH eH lH3.01 0.05 0.05 3.06 2.96 eA eA eA

39 lHb -32.07 65.62 8,412

3.02 0.35 1.10 3.37 1.92 eA eA eA0.394 0.036 0.036 0.430 0.358 mA mA mA

40 HNb -32.78 62.82 74,590

-33.54 59.73 3.70 0.04 0.05 3.74 3.65 eH lN eH-35.48 55.30 1.96 0.15 0.15 2.11 1.81 eA eA eA

41 eAb -36.83 52.81 4,172

-38.88 51.92 3.11 0.28 1.10 3.39 2.01 eA lH eA

0.098 0.011 0.011 0.109 0.087 lA lA lA

42 eHv -41.92 254.04 7,631

3.59 0.08 0.16 3.67 3.43 lH eH lH

0.935 0.073 0.073 1.01 0.862 mA mA mA

43 eNhm -45.19 43.33 53,860

3.99 0.03 0.04 4.02 3.95 eN eN eN3.87 0.02 0.02 3.89 3.85 mN mN mN3.46 0.02 0.03 3.48 3.43 lH lH lH

44 eHb -45.99 86.77 36,310

3.78 0.03 0.04 3.81 3.74 lN lN lN3.34 0.05 0.07 3.39 3.27 eA lH eA

45 eNhm -52.52 106.74 26,810

4.11 0.06 0.11 4.17 4.00 eN eN eN3.31 0.09 0.18 3.40 3.13 eA lH eA

Table 2. Assigned model ages1 for selected Mars global map units—Continued

1.00.1

10.5 2 5 

4

1.00.1

10.5 2 5 

1

1.00.1

10.5 2 5 

1.

1.00.1

10.5 2 5 

3

1.00.1

10.5 2 5 

24

1.00.1

10.5 2 5 

52

1.00.1

10.5 2 5 

25

1.00.1

10.5 2 5 

27

1.00.1

10.5 2 5 

28
31

Locality 

Number2

Unit 

label

Center coordinates 

of counting area3

Area 

(km2)

Age (Ga) Epoch4 Resurfacing grap

lat °N. long °E. best fit error + error - max. fit min. fit best fit max. fit min. fit

46 lNv -56.66 68.40 60,380

3.89 0.08 0.21 3.97 3.68 mN eN eH3.67 0.04 0.05 3.71 3.62 eH eH eH

47 lNv -57.05 35.18 26,420

3.78 0.05 0.08 3.83 3.70 lN lN eH2.54 0.28 0.30 2.82 2.24 eA eA eA

48 Hp -73.21 301.28 33,160

3.76 0.02 0.03 3.78 3.74 lN lN lN3.57 0.01 0.01 3.58 3.56 lH lH lH

1Crater size-frequency distribution model absolute age and Martian epoch fits using production function of Ivanov (2001) and epoch boundaries in the Neukum chronology 

system as defined by Michael (2013) (see table 1 for epoch boundaries, Age Determinations section for discussion, and Platz and others (2013) for detailed analysis). Each agfit is shown on separate rows, where the oldest fit reflects the age of the unit in most cases (except for crater localities 3, 9, 15, 21, 34, 39, 44, 46, and 48). For locality 18, the first two age fits apply to unit HNt, which is a composite unit.

2Crater counting localities are documented in figure 1.3Center coordinates of counting area; multiple coordinates indicate multiple subareas.4N, Noachian; H, Hesperian; A, Amazonian; e, Early; m, Middle; l, Late.5Resurfacing graphs give an at-a-glance impression of both crater density and resurfacing history (crater loss at lesser diameters) (see Platz and others, 2013). They show 

cumulative crater density per million square kilometers (gray digits, rounded to two significant figures) at a given reference diameter (heavy black mark on axis) and plot relative crater density in a given reference diameter interval with respect to the predicted value, based on the observed density at the next larger reference diameter (assuming the Ivanov, 2001, production function). Vertical axis shows the degree of resurfacing at a given diameter, where a value of 1.0 indicates no resurfacing, and a value of 0.1 indicatthat 90 percent of the craters have been erased. The value is the ratio of the observed number of craters in the diameter interval to the number predicted from the observed nuber in the next larger interval using the Ivanov (2001) production function (Platz and others, 2013).

Table 2. Assigned model ages1 for selected Mars global map units—Continued

1.00.1

10.5 2 5 

3

1.00.1

10.5 2 5 

6

1.00.1

10.5 2 5 

7.
32

Unit name Unit 

label

Area 

(106

 km2)

N(1) Error N(2) Error N(5) Error N(16) Error

LOWLAND UNITS

Middle Amazonian lowland 

unit

mAl 3.13 1,544.9 22.2 489.5 12.5 121.0 6.2 23.3 2.7

Late Hesperian lowland unit lHl 17.28 1,573.5 9.5 512.4 5.4 109.7 2.5 23.8 1.2

POLAR UNITS

Late Amazonian polar cap 

unit

lApc 0.70 14.3 4.5 11.5 4.1 10.0 3.8 7.2 3.2

Late Amazonian polar dunes 

unit

lApd 0.30 163.4 23.3 103.4 18.6 46.7 12.5 3.3 3.3

Amazonian polar undivided 

unit

Apu 2.00 271.3 11.7 143.6 8.5 76.6 6.2 32.0 4.0

Amazonian polar unit Ap 0.22 808.2 60.6 254.3 34.0 113.5 22.7 22.7 10.2

Hesperian polar unit Hp 1.35 3378.2 50.0 997.4 27.2 233.6 13.1 62.1 6.8

Hesperian polar undivided 

unit

Hpu 0.03 465.5 116.4 436.4 112.7 87.3 50.4 0.0 0.0

Hesperian polar edifice unit Hpe 0.28 795.4 53.6 412.2 38.6 162.7 24.3 32.5 10.8

BASIN UNITS

Early Amazonian basin unit eAb 0.54 1,286.6 48.7 309.2 23.9 75.5 11.8 9.2 4.1

Late Hesperian basin unit lHb 0.92 939.2 32.0 415.2 21.2 132.6 12.0 20.7 4.7

Early Hesperian basin unit eHb 0.42 1,649.2 62.6 535.5 35.7 188.0 21.2 38.1 9.5

Hesperian and Noachian 

basin unit

HNb 0.66 1,361.1 45.5 583.3 29.8 203.6 17.6 53.2 9.0

VOLCANIC UNITS

Late Amazonian volcanic 

unit

lAv 3.43 551.8 12.7 203.9 7.7 72.5 4.6 19.5 2.4

Late Amazonian volcanic 

field unit

lAvf 0.31 192.7 24.9 96.4 17.6 35.3 10.7 9.6 5.6

Amazonian volcanic unit Av 2.16 772.6 18.9 255.8 10.9 74.5 5.9 7.4 1.9

Amazonian and Hesperian 

volcanic unit

AHv 13.33 1,303.3 9.9 339.1 5.0 85.2 2.5 16.4 1.1

Late Hesperian volcanic unit lHv 2.47 2171.5 29.7 509.7 14.4 98.4 6.3 15.4 2.5

Late Hesperian volcanic field 

unit

lHvf 0.44 1670.2 61.6 402.18 30.3 111.5 15.9 15.9 6.0

Early Hesperian volcanic 

unit

eHv 6.24 2,960.1 21.8 820.3 11.5 246.7 6.3 73.4 3.4

Late Noachian volcanic unit lNv 2.45 2,213.9 30.1 804.8 18.1 258.7 10.3 74.3 5.5

Amazonian volcanic edifice 

unit

Ave 0.82 457.7 23.6 97.4 10.9 15.8 4.4 0.0 0.0

Hesperian volcanic edifice 

unit

Hve 0.38 2,230.0 76.4 568.0 38.6 175.4 21.4 28.8 8.7

Noachian volcanic edifice 

unit

Nve 0.21 2,658.4 113.7 845.6 64.1 330.5 40.1 34.0 12.9

APRON UNITS

Late Amazonian apron unit lAa 0.28 158.0 23.6 63.2 14.9 14.0 7.0 0.0 0.0

Table 3. Total crater densities for map units on Mars, based on intersection of crater center points with unit outcrops.

[Crater data are from Robbins and Hynek (2012). N(x) = number of craters > x km in diameter/counting area (in units of 106 km2). Error = (number of craters > x 

km in diameter) 0.5 / counting area (in units of 106 km2). The impact unit is not included but has been assimilated into underlying map units to more accurately and 

completely measure their crater densities. See Age Determinations section and table 5 for how these data relate to unit ages]
33

Unit name Unit 

label

Area 

(106

 km2)

N(1) Error N(2) Error N(5) Error N(16) Error

APRON UNITS—continued

Amazonian apron unit Aa 0.99 130.7 11.5 71.4 8.5 18.1 4.3 2.0 1.4

Amazonian and Noachian 

apron unit

ANa 0.38 1,017.7 51.5 481.5 35.4 195.2 22.2 44.2 10.7

TRANSITION UNITS

Amazonian and Hesperian 

transition undivided unit

AHtu 2.23 614.5 16.6 230.7 10.2 62.8 5.3 6.7 1.7

Hesperian transition undivided unit

Htu 0.75 2,262.8 54.8 608.4 28.4 176.3 15.3 37.1 7.0

Late Hesperian transition 

unit

lHt 2.40 1,950.2 28.5 549.7 15.1 160.6 8.2 33.3 3.7

Early Hesperian transition 

unit

eHt 3.95 2,715.1 26.2 848.2 14.7 238.7 7.8 50.9 3.6

Hesperian transition unit Ht 0.91 1,191.6 36.2 479.5 22.9 184.3 14.2 66.9 8.6

Hesperian transition outflow 

unit

Hto 1.35 1,868.6 37.1 481.4 18.9 130.7 9.8 32.5 4.9

Hesperian and Noachian 

transition unit

HNt 3.15 2,557.4 28.5 906.7 17.0 328.0 10.2 99.6 5.6

HIGHLAND UNITS

Hesperian and Noachian 

highland undivided unit

HNhu 1.07 3,125.4 54.1 1185.5 33.3 379.5 18.9 109.6 10.1

Noachian highland undivided 

unit

Nhu 1.65 1,667.3 31.7 504.1 17.4 148.5 9.5 39.2 4.9

Early Hesperian highland 

unit

eHh 1.89 2,730.9 38.0 727.6 19.6 181.8 9.8 32.3 4.1

Late Noachian highland unit lNh 8.98 3,646.9 20.1 1183.8 11.5 385.3 6.5 116.0 3.6

Middle Noachian highland 

unit

mNh 34.80 4,172.3 11.0 1487.1 6.5 581.1 4.1 177.4 2.3

Early Noachian highland unit eNh 15.33 3,877.3 15.9 1481.7 9.8 665.4 6.6 249.2 4.0

Noachian highland edifice 

unit

Nhe 0.22 3,894.6 132.9 1459.9 81.4 702.8 56.4 172.3 27.9

Middle Noachian highland 

massif unit

mNhm 1.97 2,669.1 36.8 1134.5 24.0 468.7 15.4 147.3 8.6

Early Noachian highland 

massif unit

eNhm 1.98 2,707.9 37.0 1231.9 24.9 598.3 17.4 217.9 10.5

Table 3. Total crater densities for map units on Mars, based on intersection of crater center points with unit outcrops.—Continued
34

Table 4. Impact craters and basins (and possible impact-like features of other origin) on Mars >150 km in diameter totaling 101 in number, 

from largest to smallest, as identified by Robbins and others (2013).

 [One feature in their database located at lat 29.9° S., long 168.6° E. is an error (S.J. Robbins, personal commun., 2013) and is not included in this table. Crater 

names are from the International Astronomical Union where available (see http://planetarynames.wr.usgs.gov/); for some unnamed craters (---), the name of a 

chaos feature within the crater is indicated in parentheses. Crater ages are chronostratigraphic period and epoch designations: N, Noachian; H, Hesperian; e, Early; 

m, Middle; l, Late. Age basis provides the primary basis for the age assignments, including crater counts in table 2, Werner (2008), and Irwin and others (2013); 

stratigraphic relations; and crater densities, where N(5 or 16) equals the number of superposed craters ≥5 or 16 km diameter per 106 km2 using the database of 

Robbins and Hynek (2012). The unit(s) column shows how we mapped preserved and, in some cases, overlying surfaces of the impact features. See text for further 

discussion]

Crater name Diameter (km) Latitude (°N.) Longitude (°E.) Crater age Age basis Unit(s)

Hellas basin ~2,400 –42 71 eN table 2 eNhm

Isidis basin ~1,500 13 89 mN N(16)=185±20 mNhm

Argyre basin ~900 –50 318 mN N(16)=133±10 mNhm

Huygens 467 –13.9 55.6 eN Werner (2008) eNh

Schiaparelli 446 –2.5 16.8 mN N(16)=187±55 mNh

--- 427 –36.8 2.8 eN N(16)=302±47 eNh

Cassini 408 23.4 32.1 eN N(16)=213±38 eNh

Antoniadi 401 21.4 60.8 eN superposed by 

Baldet

eNh

---* 376 36.7 192.4 ~N map unit HNt

Dollfus 359 –21.6 356.2 eN N(16)=351±88 eNh, mNh

Tikhonravov 344 13.3 35.9 eN N(16)=334±54 eNh

---* 341 –58.8 283.2 eN/mN map unit mNh

---* 340 23.5 53.2 eN map unit eNh

---* 327 –52.7 250.5 eN map units eNh, mNh, AHi

--- 326 –0.4 28.9 eN N(16)=229±45 eNh, mNh, AHi

Newton 312 –40.4 201.9 eN N(16)=212±57 eNh, mNh

de Vaucouleurs 312 –13.3 171.1 mN Werner (2008) eNh, mNh

--- 302 –59.9 275.9 eN N(16)=235±65 eNh, mNh

Copernicus 302 –48.8 191.2 eN Werner (2008) eNh

Herschel 298 –14.5 129.9 mN N(16)=154±40 mNh

Schroeter 292 –1.9 56.0 mN N(16)=119±38 mNh

Koval’sky 285 –29.6 218.6 eN map unit eNh

---* 285 12.9 41.9 eN buried mNh

--- 279 54.4 82.0 H/N buried lHl

--- (Aram Chaos) 276 2.8 338.8 mN N(16)=196±49 mNh

Orcus Patera 263 14.2 178.6 lN N(5)=343±83 lNh

---* 261 –4.3 333.1 N buried Ht, mNh

--- (Atlantis 

Chaos)

261 –34.4 182.4 eN N(16)=299±86 eNh

--- 257 –58.5 265.5 eN N(16)=224±56; 

degraded

eNh, mNh

Newcomb 256 –24.2 1.1 eN N(16)=229±57 eNh

---* (Gorgonum 

Chaos)

250 –37.7 189.3 eN degraded eNh, mNh

Flaugergues 236 –16.8 19.2 mN map unit mNh

--- 229 –50.1 243.1 eN N(16)=282±92 eNh, AHi
35

Crater name Diameter (km) Latitude (°N.) Longitude (°E.) Crater age Age basis Unit(s)

Galle 223 –50.6 329.1 eA N(5)=43±16 to 

55±18

AHi

Kepler 222 –46.7 141.2 eN N(16)=285±62 eNh

Lyot 220 50.5 29.3 eA Werner (2008) AHi

---* 218 43.7 18.4 N buried, degraded eHt, lNh, ANa

Secchi 217 –57.8 102.0 mN N(16)=103±46 mNh

---* 215 11.7 0.8 eN buried eNh, mNh

---* 211 –41.8 130.9 eN degraded eNh, mNh

Vinogradov 210 –19.8 322.3 eN N(16)=253±64 eNh

---* 204 –42.8 215.0 eN degraded eNh, mNh

---* 202 47.9 89.8 N/H buried lHl

Kaiser 202 –46.2 19.1 eN N(16)=339±71 eNh

Schmidt 201 –72.0 281.9 eN N(16)=226±100 eNh

--- 199 –71.1 314.2 eN N(16)=331±162 eNh

Lowell 199 –52.0 278.6 eH Werner (2008) AHi

Schöner 199 19.9 50.7 eN N(16)=436±115 eNh, mNh

Mutch 199 0.6 304.8 mN N(16)=159±88 mNh

---* 199 –9.1 20.5 eN degraded eNh, mNh

---* 197 –38.2 197.5 eN degraded eNh, mNh

---* 197 –21.1 217.0 eN degraded, buried eNh, AHv

---* 195 –31.1 293.7 mN? degraded, buried mNh, lNh

---* 195 41.8 21.9 mN? degraded, buried mNh, eHt, ANa

---* 194 –41.6 237.4 eN degraded, deformed

eNh

---* 190 31.1 186.8 N degraded, buried HNt, lAv

--- 189 –48.3 196.7 eN N(16)=472±193 eNh, mNh

Phillips 185 –66.3 315.2 mN map unit mNh

Dawes 185 –9.1 38.1 eN map unit eNh

Green 182 –52.3 351.5 lN N(5)=270±75 lNh

Baldet 181 22.8 65.5 mN N(16)=209±104 mNh, AHi

---* 180 –39.3 76.8 N buried eHb, lHb

Savich 179 –27.5 96.1 eN N(16)=655±258 eNhm, mNh, eHv, AHi

---* 179 –11.5 356.0 eN N(16)=477±229; 

buried

mNh

---* 177 –37.5 19.1 eN degraded eNh, mNh

Darwin 176 –57.0 341.0 eN N(16)=241±73 eNh

Molesworth 175 –27.5 149.2 eN N(16)=403±212 eNh

Wallace 175 –52.4 110.9 eN N(16)=241±141 eNhm

--- 175 –23.1 8.5 eN N(16)=627±189 eNh, mNh

Flammarion 174 25.2 48.3 eN N(16)=209±106 eNh, mNh

Terby 171 –28 74.1 eN N(16)=426±219 eNhm, mNh, lNh

---* 171 –23.7 30.4 eN degraded eNh, AHi

Table 4. Impact craters and basins (and possible impact-like features of other origin) on Mars >150 km in diameter totaling 101 in number, 

from largest to smallest, as identified by Robbins and others (2013).—Continued
36

Table 4. Impact craters and basins (and possible impact-like features of other origin) on Mars >150 km in diameter totaling 101 in number, 

from largest to smallest, as identified by Robbins and others (2013).—Continued

Crater name Diameter (km) Latitude (°N.) Longitude (°E.) Crater age Age basis Unit(s)

--- 169 –63.2 167.9 eN N(16)=620±235 eNh, lNh

Henry 168 10.8 23.4 eN N(16)=248±157 eNh

Proctor 167 –47.6 29.7 eN N(16)=409±262 eNh, mNh, lNh

---* 167 –23.2 219.7 eN degraded, buried eNh, Nve

--- 166 –18.2 1.6 eN N(16)=259±136 eNh, mNh

---* 166 1.8 125.4 eN/mN degraded mNh, HNt

Becquerel 165 21.9 352.1 lN N(5)=295±85 lNh

Ptolemaeus 165 –45.9 202.3 eN N(16)=256±148 eNh

--- 164 3.2 308.0 eN N(16)=284±128 eNh, AHi

Stoney 161 –69.6 221.6 eN N(16)=376±213 eNh

Denning 160 –17.4 33.5 eN N(16)=483±141 eNh, AHi

--- 159 30.6 9.1 eN N(16)=374±205 eNh

Schaeberle 159 –24.4 50.2 eN N(16)=439±235 eNh

---* 158 –26.8 193.0 eN degraded eNh, mNh

Gusev 158 –14.5 175.5 eN N(16)=899±345 eNh, mNh

Mariner 157 –34.7 195.8 eN N(16)=587±254 eNh

Lohse 155 –43.2 343.4 mN N(16)=104±81 mNh

Gale 154 –5.4 137.8 eH N(5)=173±45 AHi

--- 154 –51.5 231.5 eN N(16)=405±159 eNh

--- 154 –20.2 191.9 eN N(16)=598±241 eNh, mNh

Janssen 154 2.7 37.6 mN N(16)=117±84 mNh

Bakhuysen 153 –23.0 15.8 eH N(5)=151±36 AHi

---* 153 –54.7 244.6 eN buried eNh, mNh, lNh

Holden 153 –26.0 326.0 eH/lH Irwin and Grant 

(2013)

AHi

Arago 152 10.2 29.9 eN N(16)=455±254 eNh, mNh, AHi

Dejnev 152 –25.1 195.4 eN N(16)=253±123 eNh, AHi

---* 151 6.8 182.2 N degraded, buried HNt, lHt

--- 151 –9.0 353.1 mN map unit mNh

* The impact origin of these features is considered to be uncertain due to poorly preserved or inferred buried rims.
37

Table 5. Basis for time-stratigraphic assignments for each map unit as shown in the Correlation of Map Units. 

[Key stratigraphic relations (<, younger than; ~, coeval with; >, older than) are derived from mapping observations (see Description of Map Units for more detail). 

Crater size-frequency data are sourced from tables 2 to 4 and from within literature references (however, not all units have useful crater size-frequency data). Locality numbers refer to specific crater size-frequency data in table 2. N(x), where x = 1, 5, or 16, refers to specific crater-density values in table 3. ---, no data]

Unit label Key stratigraphic relations Crater size-frequency data

LOWLAND UNITS

mAl < lHl; > lApd, most of Apu Werner and others (2011); Skinner and others (2012)

lHl < lHt, Hto; > eAb, Av Localities 2, 6, 10, and 11; N(5); Werner and others (2011)

IMPACT UNIT

AHi < lNh ---

POLAR UNITS

lApc < Apu ---

lApd < mAl, most of Apu ---

Apu < lHl, Hpu, most of Ap; > Apu Koutnik and others (2002); Tanaka (2005); Tanaka and others 

(2008); Banks and others (2010)

Ap < Hp; > most of Apu N(1); Tanaka and Kolb (2001)

Hp < lNh; > Ap, Apu Locality 48; N(5) 

Hpu > Apu Tanaka and Fortezzo (2012)

Hpe ~ Hp, lHl; > Apu, mAl N(5) 

BASIN UNITS

eAb < lHb, lHl; ~ Av; > mAl Localities 3, 5, 41; Tanaka and others (2005)

lHb < eHb; > eAb Locality 39; N(5)

eHb < lNb; > lHb Locality 44; N(5)

HNb < mNh; ~ lNv; > eHb Locality 40; N(5) and N(16)

VOLCANIC UNITS

lAv < Av; ~ lAvf Localities 9 and 21; Tanaka and others (2005); Vaucher and others 

(2009); Hauber and others (2011)

lAvf ~ lAv Tanaka and others (2005); Vaucher and others (2009); Hauber and 

others (2011)

Av < lHl; ~ eAb; > mAl, lAv Locality 4; Tanaka and others (2005)

AHv < lHl, Hve; ~ eHv, lHv, eAb, lAvf; > Av, mAl, lAa, 

lAv

N(1) and N(5); Tanaka and others (2005); Hauber and others (2011)

lHv < eHv, eHh; > AHv, AHtu, Aa Localities 17 and 29; N(5); Dohm and others (2001a)

lHvf < eHh; ~ lHv N(5); Hauber and others (2011)

eHv < lNv, lNh; ~ eHt, eHh; > lHv, lHt, lHl Localities 38 and 42; Dohm and others (2001a)

lNv < mNh; ~lNh; > eHv, eHh, eHb Localities 46 and 47; N(5) and N(16); Tanaka and Leonard (1995); 

Dohm and others (2001a)

Ave ~ lAvf, AHv; > lAa N(1)

Hve < eNhm; ~ lHv, lHvf, lHt, lHl, eHv; > AHv N(5); Tanaka and others (1992); Tanaka and Leonard (1995); Crown 

and Greeley (2007); El Maary and others (2012)

Nve ~ lNv, mNh, eNh; > eHv, Htu N(5); Greeley and Crown (1992), Gregg and others (1998); Werner 

(2009); Xiao and others (2012)

APRON UNITS

lAa > Aa, Ave ---

Aa < Av, lHt, lHv; > lAv, lAvf, lAa N(1); Quantin and others (2004)

ANa Noachian part: ~ HNt, lNh, mNh, eNhm. Amazonian 

part: < AHv, lHt

N(1) and N(16)
38

Unit label Key stratigraphic relations Crater size-frequency data

TRANSITION UNITS

AHtu < Aa, Ave, lHv, eHv; ~ AHv; > lAv Localities 25, 27, and 30); N(5); Tanaka and others (2005); Kerber 

and Head (2010); Zimbelman and Scheidt (2012)

Htu < Nhu, Nve; ~ eHt, Hve; > lHt, Ht, Hto, AHtu Localities 26 and 28; N(5); Kerber and Head (2010); Zimbelman 

and Scheidt (2012)

lHt < eHt, eHv, eHh; ~ AHv; > Hto, lHl, AHtu Localities 8 and 15; Tanaka and others (2005)

eHt < lNh; ~ eHv, Htu, HNt; > Ht, Hto, lHl, lHt, AHtu Localities 2 and 16; Tanaka and others (2005)

Ht < eHt, eHh, eHv; ~ Hto; > Htu, lHt N(5)

Hto < AHv, lHt, eHh; ~ Ht; > lHl Locality 12; N(5); Rotto and Tanaka (1995); Tanaka (1997); Tanaka 

and others (2005); Chapman and others (2010)

HNt Noachian part: ~ eNh, mNh, lNh. Hesperian part: 

< lNv; ~ eHt, eHh, Htu, Hve; > eHv, lHt, lHl, 

AHtu

Locality 18; N(1), N(5), and N(16); Tanaka and others (2005)

HIGHLAND UNITS

HNhu < eHh, lNh; ~ eHb; > eHv Locality 24; N(5) and N(16); Hynek and Phillips (2008)

Nhu ~ lNh, lNv, mNh, eNh; > eHt, eHv, eHt Locality 37; Dohm and others (2001a)

eHh < lNh, lNv; ~ eHv; > Hto, lHv, lHvf, lHt N(5)

lNh < mNh, mNhm; ~ lNv; > eHv, eHh, eHt, eHb Localities 13, 34, and 35; N(5) and N(16); Dohm and others (2001a)

mNh < eNh, eNhm; ~ mNhm; > lNh, lNv Localities 7, 14, 19, 20, 22, 23, and 31; N(5) and N(16)

eNh ~ eNhm; > mNhm, mNh Localities 32 and 36; N(16)

Nhe ~ lNh, mNh, eNh; > lNh, lNv N(5) and N(16); Xiao and others (2012)

mNhm ~ mNh, eNh; > lNh N(5) and N(16); N(16) for Isidis and Argyre basins; Robbins and 

others (2013)

eNhm ~ eNh; > mNh Localities 43 and 45; N(16); Robbins and others (2013)

Table 5. Basis for time-stratigraphic assignments for each map unit as shown in the Correlation of Map Units. —Continued
39

Table 6. Percentages of previously mapped Viking-based map units for each unit in this Mars global map; values <5 percent not shown. 

[Former mapping from digital map of Skinner and others (2006), which was adapted from Scott and Tanaka (1986), Greeley and Guest (1987), and Tanaka and Scott 

(1987)]

Global map unit name, this map Unit label Area 

(106

 km2)

Previously mapped Viking-based units 

(% intersect)

POLAR UNITS

Middle Amazonian lowland unit mAl 3.09 Am (21), Hvk (20), Hvm (18), Apk (14), Hvg (6), HNu (6)

Late Hesperian lowland unit lHl 16.11 Hvk (31), Hvm (16), Aa1

 (11), Hvg (11), Hvr (8), Apk (6), Am (5)

IMPACT UNIT

Amazonian and Hesperian impact unit AHi 7.83 cs (35), Npl1

 (17), Hr (7), Npld (7), Npl2 (5)

POLAR UNITS

Late Amazonian polar cap unit lApc 0.70 Api (82), Apl (18)

Late Amazonian polar dunes unit lApd 0.30 Adl (66), Adc (28), Am (5)

Amazonian polar undivided unit Apu 2.01 Apl (79), Api (10)

Amazonian polar unit Ap 0.22 Hnu (53), Hdl (24), Hdu ( 14), Am (5)

Hesperian polar unit Hp 1.22 Hdu (53), Hdl (21), HNu (9), Npl2

 (7)

Hesperian polar undivided unit Hpu 0.03 Apl (52), Am (32), Hvg (14)

Hesperian polar edifice unit Hpe 0.26 Am (55), HNu (14), Api (9), Nplh (5)

BASIN UNITS

Early Amazonian basin unit eAb 0.55 Ael3

 (77), Hvg (9)

Late Hesperian basin unit lHb 0.91 Hh3

 (69), Hh2 (14), Ah8 (13)

Early Hesperian basin unit eHb 0.40 Hh2

 (77), Hh3 (21)

Hesperian and Noachian basin unit HNb 0.60 Hh2

 (28), Nple (27), Hpl3 (20), Hr (8), Ah7 (7), Ah6 (5)

VOLCANIC UNITS

Late Amazonian volcanic unit lAv 3.23 Aa3

 (34), Achu (22), Aop (9), Aa4 (7), Aps (5)

Late Amazonian volcanic field unit lAvf 0.30 Aps (21), At5

 (18), At6 (16), AHcf (11), Aop (11), Apk (10), 

Achu (7)

Amazonian volcanic unit Av 2.02 Ael3

 (37), Aa4 (18), Aa3 (13), Aa1 (7)

Amazonian and Hesperian volcanic unit AHv 13.44 At5

 (21), Ael1 (15), Hal (13), At4 (9), Aam (8), AHt3 (6), At6 (5)

Late Hesperian volcanic unit lHv 2.41 Hsu (36), Hsl (20), Hf (15), Hf (9), Hr (7)

Late Hesperian volcanic field unit lHvf 0.45 Hsu (26), Ael1

 (24), Htu (15), AHcf (8), Ht2 (6), Htm (6)

Early Hesperian volcanic unit eHv 5.83 Hr (42), Hs (22), Hpl3

 (8), Nf (5)

Late Noachian volcanic unit lNv 2.32 Hr (49), Had (19), Nplr (7), Hh2

 (5)

Amazonian volcanic edifice unit Ave 0.83 Aos (43), AHt3

 (37), Aau (15)

Hesperian volcanic edifice unit Hve 0.37 v (25), Ael2

 (23), Ahh (23), Ael1 (9), Hhet (6), AHa (5), AHat (5)

Noachian volcanic edifice unit Nve 0.16 Hr (22), AHt (21), Had (20), Hap (13), AHa (13)

Late Amazonian apron unit lAa 0.29 As (87), AHt3

 (5)

Amazonian apron unit Aa 0.99 Aoa1

 (40), Aoa4 (24), Aoa3 (13), Aoa2 (7), Ae (5)

Amazonian-Noachian apron unit ANa 0.28 As (53), HNu (9), Hr (7), Hch (7)

TRANSITION UNITS

Amazonian and Hesperian transition 

undivided unit

AHtu 2.20 Amu (43), Amm (26), Aml (15)

Hesperian transition undivided unit Htu 0.50 Aml (28), Amm (23), Hvl (11), Avf (7), Achu (7), Apk (6), HNu

(5), Npl2

 (5)

Late Hesperian transition unit lHt 2.37 Aa1

 (29), Aps (20), Hr (13), Apk (12)
40

Global map unit name, this map Unit label Area 

(106

 km2)

Previously mapped Viking-based units 

(% intersect)

Early Hesperian transition unit eHt 3.72 Hr (40), AHpe (11), Apk (10), Aa1

 (8), Aps (7), HNu (7), Npld (5)

Hesperian transition unit Ht 0.91 Hcht (58), Hch (14), Npl2

 (7)

Hesperian transition outflow unit Hto 1.28 Hch (33), Hchp (33), Aa1

 (19), Hr (12)

Hesperian and Noachian transition unit HNt 2.81 HNu (48), Apk (13), Aa1

 (8), Npl2 (5)

HIGHLAND UNITS

Hesperian and Noachian highland undivided unit

HNhu 0.36 Npl2

 (47), Ah5 (21), Nple (6), Hpl3 (5)

Noachian highland undivided unit Nhu 2.54 Hch (24), HNu (20), Hchp (14), Npl1

 (8), Npl2 (5), Hr (5), Nf (5)

Early Hesperian highland unit eHh 1.84 Hr (70), Hf (7), Npl2

 (6)

Late Noachian highland unit lNh 8.78 Hr (29), Hpl3

 (16), Npl2 (12), Npl1 (10), Nplr (7), Npld (6)

Middle Noachian highland unit mNh 30.41 Npl1

 (32), Npld (22), Npl2 (14), Hr (8), Nplr (7)

Early Noachian highland unit eNh 16.05 Npl1

 (36), Npld (30), Nplr (8), Npl2 (5)

Noachian highland edifice unit Nhe 0.21 Npl1

 (22), v (19), Nf (16), Nb (10), Nplh (7), Npl2 (6), Hr (5)

Middle Noachian highland massif unit mNhm 1.86 Nplh (57), Hpl3

 (15), Npld (11), Npl2 (6)

Early Noachian highland massif unit eNhm 1.95 Nh1

 (67), Nm (11), Npl2 (11)

Table 6. Percentages of previously mapped Viking-based map units for each unit in this Mars global map; values <5 percent not shown. —

continued
41

Table 7. Percentages of map units in this Mars global map for each previously mapped Viking-based map unit; values <5 percent not 

shown. Units organized as in Tanaka and others (1988, table 1)

[Former mapping from digital map of Skinner and others (2006), which was adapted from Scott and Tanaka (1986), Greeley and Guest (1987), and Tanaka and Scott 

(1987)]

Previously mapped Viking-based unit 

name

Unit label Area

 (106

 km2)

Global map units, this map (% interscet) 

SURFICIAL MATERIALS

eolian deposits Ae 0.16 AHtu (50), Aa (32), lAv (16)

dune material Ad 0.01 lNh (47), eNh (27), HNhu (11), Apu (9), mNh (5)

crescentic dune material Adc 0.46 lHl (66), lApd (18), Apu (8), mAl (7)

linear dune material Adl 0.23 lApd (87), Apu (7), Hpe (5)

mantle material Am 1.76 lHl (50), mAl (36), Hpe (8)

slide material As 0.62 lAa (40), ANa (27), mNh (5), AHi (5)

polar ice deposits Api 0.96 lApc (60), Apu (21), lHl (14)

polar layered deposits Apl 1.84 Apu (87), lApc (7)

CHANNEL-SYSTEM MATERIALS

younger channel material Ach 0.01 mAl (52), mNh (34), lHl (8)

older channel material Hch 1.46 Hto (29), Nhu (27), mNh (10), Ht (9), eHt (6)

younger flood-plain material Achp 0.05 lAv (83), eHt (11), lAv (5)

older flood-plain material Hchp 1.05 Hto (40), Nhu (22), lNh (10), AHv (10)

chaotic material Hcht 0.81 Ht (66), HNt (13), mNh (8)

younger channel system material, undivided

Achu 0.97 lAv (78), Htu (5), AHtu (5)

channel bar b 0.04 Hto (40), Nhu (32), AHv (11), mNh (7)

LOWLAND TERRAIN MATERIALS

Northern plains assemblage

Arcadia Formation, member 5 Aa5 0.21 Av (37), lAv (29), lHt (21), lHl (11)

Arcadia Formation, member 4 Aa4 0.67 Av (58), lAv (36)

Arcadia Formation, member 3 Aa3 1.74 lAv (67), Av (16), AHv (11)

Arcadia Formation, member 2 Aa2 0.14 Av (56), lHl (40)

Arcadia Formation, member 1 Aa1 3.94 lHl (47), lHt (17), eHt (7), AHv (7), Hto (6), HNt (6)

Medusae Fossae Formation, upper member Amu 1.00 AHtu (94)

Medusae Fossae Formation, middle 

member

Amm 0.89 AHtu (63), Htu (19), HNt (6), lHt (5)

Medusae Fossae Formation, lower member Aml 0.61 AHtu (54), Htu (33), HNt (7)

Vastitas Borealis Formation, mottled 

member

Hvm 3.27 lHl (79), mAl (17)

Vastitas Borealis Formation, grooved 

member

Hvg 2.10 lHl (88), mAl (8)

Vastitas Borealis Formation, ridged 

member

Hvr 1.38 lHl (94)

Vastitas Borealis Formation, knobby 

member

Hvk 5.93 lHl (84), mAl (10), AHi (5)

smooth plains material Aps 2.51 lHl (24), lHt (19), AHv (13), eHt (11), lAv (8), eHv (6), AHi (6), 

mAl (5)

etched plains material AHpe 0.47 eHt (87), HNt (5)
42

Previously mapped Viking-based unit 

name

Unit label Area

 (106

 km2)

Global map units, this map (% interscet) 

Eastern volcanic assemblage

Elysium Formation, member 4 Ael4 0.06 Av (77), eAb (9), AHv (9)

Elysium Formation, member 3 Ael3 1.33 Av (58), eAb (31)

Elysium Formation, member 2 Ael2 0.09 Hve (91), lHvf (5)

Elysium Formation, member 1 Ael1 2.58 AHv (78), lAv (9)

Albor Tholus Formation AHat 0.02 Hve (96)

Hecates Tholus Formation Hhet 0.03 Hve (95)

Syrtis Major Formation Hs 1.35 eHv (95)

dome d 0.01 mAl (69), Hpe (27)

HIGHLAND TERRAIN MATERIALS

Western volcanic assemblage

Olympus Mons Formation, plains member Aop 0.45 lAv (71), AHv (9), lAvf (8), AHtu (6)

Olympus Mons Formation, shield member Aos 0.38 Ave (93)

Olympus Mons Formation, aureole member 4

Aoa4 0.24 Aa (100)

Olympus Mons Formation, aureole member 3

Aoa3 0.13 Aa (96)

Olympus Mons Formation, aureole member 2

Aoa2 0.08 Aa (91), lAvf (5)

Olympus Mons Formation, aureole member 1

Aoa1 0.47 Aa (86), AHtu (13)

Tharsis Montes Formation, member 6 At6 0.67 Ahv (91), lAvf (5)

Tharsis Montes Formation, member 5 At5 2.99 AHv (92)

Tharsis Montes Formation, member 4 At4 1.21 AHv (94)

Tharsis Montes Formation, member 3 AHt3 1.23 AHv (63), Ave (25)

Tharsis Montes Formation, member 2 Ht2 0.62 AHv (88), lHvf (5)

Tharsis Montes Formation, member 1 Ht1 0.18 Ahv (89), AHi (8)

Alba Patera Formation, upper member Aau 0.19 Ave (65), Ahv (35)

Alba Patera Formation, middle member Aam 1.00 AHv (100)

Alba Paterae, lower member Hal 1.90 AHv (92)

Ceraunius Fossae Formation Ahcf 0.47 AHv (73), lAv (8), lAvf (7), lHvf (7)

Syria Planum Formation, upper member Hsu 1.35 lHv (63), AHv (14), lHvf (9), eHv (8)

Syria Planum Formation, lower member Hsl 0.59 lHv (81), eHv (16)

Hellas assemblage

knobby plains floor unit Ah8 0.12 lHb (98)

rugged floor unit Ah7 0.09 HNb (44), mNh (33), lNv (14), eAb (8)

reticulate floor unit Ah6 0.03 HNb (95), eAb (5)

channeled plains rim unit Ah5 0.46 Nhu (47), lNh (28), eHv (20),

lineated floor unit Ah4 0.04 lHb (95), eHb (5)

dissected floor unit Hh3 0.76 lHb (83), eHb (11)

ridged plains floor unit Hh2 0.81 eHb (37), HNb (21), lHb (16), lNv (13)

basin-rim unit Nh1 1.88 eNhm (69), mNh (15), eNh (8)

Table 7. Percentages of map units in this Mars global map for each previously mapped Viking-based map unit; values <5 percent not 

shown.—Continued
43

Previously mapped Viking-based unit 

name

Unit label Area

 (106

 km2)

Global map units, this map (% interscet) 

Plateau and high-plains assemblage

Valles Marineris interior deposits, floor 

material

Avf 0.21 lHt (32), HNhu (25), Nhu (16), Ht (14), Aa (11)

Valles Marineris interior deposits, layered 

material

Hvl 0.09 HNhu (86), Nhu (7), lHt (5)

Tyrrhena Patera Formation AHt 0.05 Nve (90), eHv (10)

Apollinaris Patera Formation AHa 0.06 Nve (46), Hve (34), HNt (12)

Hadriaca Patera Formation AHh 0.12 Hve (75), eHv (27)

Amphitrites Formation, patera member Hap 0.12 lNv (77), Nve (23)

Amphitrites Formation, dissected member Had 0.48 lNv (89), Nve (9)

Tempe Terra Formation, upper member Htu 0.22 eHv (46), lHvf (31), lNh (7), eHh (6)

Tempe Terra Formation, middle member Htm 0.21 eHv (50), lHv (19), lHvf (13), AHv (6)

Tempe Terra Formation, lower member Htl 0.04 mNh (56), lHvf (21), eHv (16), AHi (8)

highly-deformed terrain materials, younger 

fractured material

Hdu 0.84 Hp (78), Apu (7)

Dorsa Argentea Formation, upper member Hdl 0.49 Hp (52), lNh (14), mNh (12), Ap (11), Apu (5)

plateau sequence, smooth unit Hpl3 3.66 lNh (37), mNh (18), eHv (13), mNhm (8), AHi (5)

plateau sequence, mottled smooth plains 

unit

Hplm 0.30 lNh (43), mNh (25), eNh (23)

plateau sequence, subdued cratered unit Npl2 8.24 mNh (56), lNh (12), eNh (8), HNhu (6), AHi (5)

plateau sequence, cratered unit Npl1 18.54 mNh (56), eNh (28), AHi (7)

plateau sequence, dissected unit Npld 13.38 mNh (53), eNh (32)

plateau sequence, etched unit Nple 2.59 mNh (50), eNh (23), HNb (6), AHi (5)

plateau sequence, ridged unit Nplr 4.61 mNh (53), eNh (25), lNh (13)

plateau sequence, hilly unit Nplh 2.61 mNhm (41), eNh (24), mNh (19), AHi (5)

younger fractured material Hf 1.23 lHv (28), mNh (10), eHh (9), lNh (6), AHi (5), Nhu (5)

highly-deformed terrain materials, older 

fractured material

Nf 1.52 mNh (26), eHv (19), lNh (17), lHv (14), AHv (5), Nhu (5), eHh

(5), eNh (5)

highly-deformed terrain materials, basement complex

Nb 0.29 mNh (38), eNh (25), AHv (8), Nhe (8), Nhu (7), lNh (6)

undivided material HNu 3.21 HNt (44), Nhu (10), eHt (8), lHl (6), mAl (5)

volcano (relative age unknown) v 0.31 Hve (31), eHv (19), Nhe (14), mNh (12), eNh (10), AHv (6)

mountain material Nm 0.36 eNhm (61), eHv (7), eNh (6), mNhm (5)

mountain ( relative age unknown) m 0.03 eNh (68), mNh (11), lNh (9), AHv (8)

MATERIALS THROUGHOUT MAP AREA

knobby plains material Apk 2.67 lHl (35), mAl (16), eHt (14), HNt (14), lHt (10)

ridged plains material Hr 13.56 mNh (19), eHv (18), lNh (18), eHt (11), eHh (9), lNv (8)

impact crater material, superposed cs 3.45 AHi (81), mNh (7)

impact crater material, partly buried cb 1.32 eNh (44), mNh (28), AHi (11), lNh (10)

impact crater material, smooth floor s 1.01 eNh (31), lNh (22), mNh (17), AHi (13)

Table 7. Percentages of map units in this Mars global map for each previously mapped Viking-based map unit; values <5 percent not 

shown.—Continued
44