–1000

–2000

–2000

–1000

–1000

–3000

–6000

–7000

–7000

–7000

–7000

–7000 –7000

–7000

–7000

–7000

–6000

–7000

–7000

–7000

–7000

–7000

–7000

–7000

–7000

–7000

–7000

–5000

–5000

–5000

–6000

–6000

–7000

0007–

–7000

–7000

–7000

–6000

–6000

–7000

–7000

–7000

–7000

–7000

–7000

–6000

–6000

–6000

–6000

–6000

–7000

–7000

–6000

–4000

–4000

–4000

–4000

–4000

–4000

–4000

–4000

–4000

–4000

–2000

–2000

–2000

–2000

–4000

–4000

–3000

–3000

–6000

As

As

AHs

AHh

Hc

Nc

Hp

Hw

Hk

Hr

Hsr

Hpl3

Hpl2

Hpl1

HNp

Npl

Nb

AHc

Hpl3

Hpl2

Hr

Hpl1

HNp

Nb Npl

AHs AHh

AHc

Hc

Nc

Hk

Hw Hp

Hsr

h

u

u

HNp

HNp

Hr

Hr

Hp

Hp

pl

c

c

c

c

c

c p

As

As HNp

HNp

HNp

HNp HNp

HNp

Hw Hc

Hk

Hr

Hr

Hp AHh

?

? ?

? ? ? ?

AHs

Hpl3

Hpl2 Hpl2

Hpl2

Hpl1

Hpl1

Hpl3 Hpl3 Hpl3

Hc

Hp

HNp

Npl

Nb

Npl

As

Nb

Hc

Hc

Hc

Hc

Hc

Hc

Hc

Hc

Hc

As

As

As

As

As

As

As

As

Hp

Hc

Hr

Hr

Hr

Nb

Nb

Nb

Nb

Hc

Nc

Nc

Nc

Nc

Nc

Nc

Nb

As

Hp

Hp

Hp

Hp

Hr

Hr

Hr

Nb

Nb

Hc

Nc

Nc

Nb

As

Nc

Nc

As

As

Hp

Hp

Hp

Nb

Nb Nb

Nb

Hc

Nc

Hr

Hr

Hc

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Npl

Nc

Npl

Npl

Nc

Npl

Hr

Hr

Hr

Hc

Hc

Hc

Nc

Hr

HNp

HNp

HNp

HNp

HNp

HNp

HNp

HNp

HNp

HNp

As?

Hr?

AHc

AHc

Hsr

Hsr

Hsr

Hsr

Hsr

Hpl1

Hpl1?

Hp

Hpl2

Hpl2

Hpl2

Hsr

Hc

Hpl3

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl2

Hpl1

Hpl1 Hpl1

Hpl3

Hpl3

Hpl3

Hpl3

Hpl3

Hpl3

Hpl1

Hpl1

Hpl3

Hpl2

Hpl3

Hpl3

Hpl3

Hpl2

Hw

Hw

Hw

Hw

Hw

Hw

Hw

Hw

Hw

Hk

Hk

Hk

Hk

Hk

Hpl3

Hpl3 (Hc)

Hk

Hc

AHs

AHh

AHs

AHs

AHs

AHs

AHh

Hsr

Hsr

Hsr

Nc

Hc

AHh

Hpl2

Hpl2

HELLAS PLANITIA Alpheus Colles

Hellespontus Montes Hellespontus Montes

Alpheus

Colles

HELLAS

Beloha

Beloha

PLANITIA

Any use of trade, product, or firm names used in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal 

Center, Denver, CO 80225, 1–888–ASK–USGS

Available at http://pubs.usgs.gov/sim/2007/2953/

Printed on recycled paper

1NASA Ames Research Center, Moffett Field, CA 94035

2U.S. Geological Survey, Menlo Park, CA 94025

BASIN-FILL MATERIAL

BASIN-RIM

MATERIAL

CRATER

MATERIAL

AMAZONIAN

NOACHIAN

HESPERIAN PERIOD

CORRELATION OF MAP UNITS

DESCRIPTION OF MAP UNITS

BASIN-FILL MATERIAL

Younger smooth material (Amazonian)—Smooth, featureless, almost uncratered. On elevated 

terrain in western map area. Interpretation: Aeolian deposits of sand and indurated dust, as 

deduced from variable, high elevations where less subject to erosion than in Hellas Planitia

Older smooth material (Amazonian or Hesperian)—Smooth, wavy, or lobate. Marginal to unit 

AHh. Interpretation: Apparently related to unit AHh, therefore probably additional lacustrine deposit, modified by flowage

Honeycomb material (Amazonian or Hesperian)—Subplanar overall, with distinctive 

cell-like, closely packed, subequal elliptical or polygonal rimmed pits a few kilometers 

across producing honeycomblike appearance; more elongate, less regular near unit edges 

(fig. 6). In depression in north-central map area. Dated as Amazonian by Leonard and Tanaka 

(2001). Interpretation: Collection in depression indicates lacustrine origin, probably 

deformed while still wet by grounding of ice blocks as lake level dropped, resulting in 

soft-sediment deformation textures and morphology (figs. 2, 7)

Younger plains material (Hesperian)—Expansive, sparsely cratered, smooth to wavy. Locally 

incised, forming scarp-bounded enclosures. Interpretation: Scarps and smoothness indicate 

thickness sufficient to bury or mantle pre-existing topography over extensive area; therefore, 

probably water-laid, not aeolian. Possibly volcanic in part

Wavy material (Hesperian)—Smooth, flat to undulatory, sparsely dotted with small (~1 km) 

knobs; flow structure visible at high resolution. Gradational with knobby material (Hk) and 

Alpheus plateau materials (Hpl3, Hpl2, Hpl1). Interpretation: Debris flows and plateau 

remnants, probably created by chaotic ground collapse caused by ice loss

Knobby material (Hesperian)—Closely spaced, roughly equidimensional knob-like hills 

typically a few kilometers across and possibly a few hundred meters high; some knobs 

elongate, some trend northeast. Occupies deep depression in southeastern map area. Interpretation: Broken from plateau materials during erosional retreat of plateau, probably 

through chaotic ground collapse caused by loss of ice matrix or substrate; elongate knobs 

possibly aeolian yardangs

Reticulate material (Hesperian)—Rough overall appearance from many short, sharp interconnected ridges connected into a net-like pattern of cells typically 1–2 km across (figs. 4, 5). 

Ridges generally tangential or normal to Hellas basin rim, enclosing rectangular or elliptical 

depressions. Main exposure lies along –5.8 km contour and concentric with basin rim. Interpretation: Deposited along periphery of ice-covered lake

Sinuous ridge material (Hesperian)—Sinuous ridges typically a few tens to ~75 km long and a 

few kilometers wide. Peripheral to Alpheus Colles plateau or superposed on units Hpl1 or 

Hpl2 (fig. 3). Interpretation: Similarity to terrestrial eskers suggests origin by flow of 

sediment-laden water under ice layer or icy sediment

Upper Alpheus plateau material (Hesperian)—Uppermost layers of plateau studded by 

Alpheus Colles hills. Relatively smooth or wavy; partially bounded by irregular scarps. 

Interpretation: All three Alpheus plateau units probably originated as water-laid sediment 

then were degraded by loss of ice matrix derived from the water medium (see discussion 

regarding degradation style and water sources)

Intermediate Alpheus plateau material (Hesperian)—Intermediate layers forming plateau. 

Rough, uneven, hilly or hummocky, bounded by irregular scarps

Lower Alpheus plateau material (Hesperian)—Lowermost layers of plateau. Irregular, rough 

hills and lumps of all sizes and distributions bounded by irregular scarps

Older plains material (Hesperian to Noachian)—Not distinctive at Viking mapping scale; 

intermediate in roughness between adjacent units Npl and As. Located on Hellas basin wall 

beneath –3.1 km contour. Interpretation: Ambiguous but consistent with deposition in 

ice-covered water body reaching –3.1 km contour

BASIN-RIM MATERIAL

Older plateau material (Noachian)—Moderate roughness on slopes or level parts of Hellas 

basin rim and wall. Interpretation: Probably mixed materials including basin ejecta, masswasted debris, and later aeolian deposits

Basin material (Noachian)—Forms mountainous massifs and other topographic prominences of 

Hellas basin rim and wall. Interpretation: Uplifted during basin-forming impact and covered 

by unknown thickness of basin ejecta

CRATER MATERIAL

Younger crater material (Amazonian or Hesperian)—Rims, flanks, floors, and outer ejecta of 

relatively fresh-appearing craters. Pedestal-like ejecta where exposed, terminating at steep 

scarp. Interpretation: Impact crater materials including ejecta blankets of a type characteristic of derivation from volatile-rich targets

Middle crater material (Hesperian)—Rims, flanks, floors, and outer ejecta of slightly degraded 

craters or small rings without visible ejecta. Interpretation: Materials of impact craters, 

eroded or nearly obscured by later deposits

Older crater material (Noachian)—Forms degraded rims or central peaks of large craters. 

Interpretation: Ancient impact crater materials

Contact—Dotted where concealed (Hc/Hpl3 contact). Queried in cross section where hypothetical

Interfingering contact (cross section)

Irregular depression—Hachures point downslope

Crater rim crest

Buried crater rim crest

Topographic contour—Negative value denotes depth in kilometers below MOLA-derived Mars 

datum

INTRODUCTION

Rock units were deposited on Mars by meteorite impact, volcanism, wind, flowing water, standing 

water, and ice, acting separately or in concert. Hellas Planitia, the deepest tract on Mars, is a broad depression 

lying within the high-rimmed, approximately 2,300-km-wide Hellas impact basin. The basin and the planitia 

are centered about 250 km east of the southeast corner of the map area. Like other stratigraphy-based 

planetary mapping (Wilhelms, 1990), we suggest the most likely origins for age relations and morphologies 

visible in the map area.

Western Hellas Planitia was first mapped geologically by Peterson (1977) using Mariner 9 images that 

barely disclosed surface detail. Greeley and Guest (1987), mapping from better Viking images but at the 

small scale of 1:15,000,000, proposed that lava flows underlie and partly constitute the deposits of Hellas 

Planitia, but that deposits exposed in the map area are sediments dissected by winds and minor fluvial activity. Kargel and Strom (1992) suggested deposits originating from continental glaciers and proglacial lakes. 

Moore and Edgett (1993) interpreted Viking and Earth-based remote-sensing data as more consistent with 

fine-grained surface material than with coarse glacial deposits or blocky volcanics. Tanaka and Leonard 

(1995) favored wind as the main agent of both deposition and erosion, which they reiterate in their 

1:5,000,000-scale mapping of the entire Hellas region (Leonard and Tanaka, 2001). Studies of areas around 

Hellas Planitia disclosed undoubted volcanic landforms (Potter, 1976; Peterson, 1977; Greeley and Guest, 

1987; Tanaka and Leonard, 1995; Leonard and Tanaka, 2001). An idea of particular interest for our map is 

that water, released by volcanism or geothermal heat from subsurface ice, carried sediment into Hellas Planitia along the large channels called Dao and Harmakhis Valles east of the map area (Squyres and others, 1987; 

Crown and others, 1992; Price, 1998), as well as in smaller but numerous channels along much of the basin 

periphery. Similarly, magmatic intrusions into erosion-prone, volatile-rich terrain now occupied by Malea 

and Hesperia Plana (east of the map area) may have triggered flows of debris into Hellas Planitia (Tanaka and 

others, 2002).

Our map is based primarily on Viking orbital images of uneven quality obtained from 1976 to 1980. This 

basic mapping was completed when, in 1999, Mars Global Surveyor (MGS) began transmitting elevation 

data from the Mars Orbiter Laser Altimeter (MOLA; Smith and others, 1999) and high-resolution images 

from the Mars Orbiter Camera (MOC; for example, Malin and Edgett, 2000). These valuable new data 

clarified geologic relations and revealed diagnostic morphologies of the already mapped units. The Viking 

and MGS data are combined here and in a report that extends the study to the rest of Hellas Planitia (Moore 

and Wilhelms, 2001). As that report explains more fully, we maintain that the geologic relations and characteristics of most mapped rock units are the result of sedimentation from ice-covered bodies of water.

STRATIGRAPHY

The rim and wall of the Hellas impact basin rise above Hellas Planitia in the west quarter of the map area 

and culminate along the map edge as the classical feature Hellespontus Montes. The rock composing the 

more rugged, massif-like topography probably shaped by the impact is mapped as basin material (unit Nb) 

and the intervening less-rugged terrain of uncertain origin is mapped as older plateau material (unit Npl). 

Both units appear smooth at fine scale on available images. This mountainous terrain is pocked by so many 

large Noachian craters (unit Nc) that the basin must have been created very early in Martian history and be 

Noachian in age. Similar terrain must extend beneath the exposed rocks of Hellas Planitia.

Hellas Planitia may be underlain by postbasin materials deposited in the Noachian Period, but the 

exposed units are probably Hesperian or perhaps early Amazonian in age (Greeley and Guest, 1987; Tanaka 

and Leonard, 1995; Leonard and Tanaka, 2001). Age assignments of individual map units are based on crater 

statistics given by Leonard and Tanaka (2001) for units identifiable as roughly conterminous with our units 

(although differently named). Extensive and differential erosion precludes more precise dating from crater 

statistics in the map area. Relative ages of adjacent units are determined from superposition and cross-cutting 

relations.

The oldest postbasin geologic map unit is older plains material (unit HNp), which is equivalent to the 

mantling material of Moore and Wilhelms (2001, unit m). Its presence is revealed by faint textural elements 

and a partial blanketing of craters and the basin wall as high as –3.1 km elevation (fig. 1; Moore and Wilhelms, 

2001). Because it reached so high, we assume that this unit also filled low elevations and interpret it on the 

cross section as the oldest postbasin unit in Hellas Planitia. It presumably would level out the irregular basin 

floor. However, other units not exposed in this map area very likely underlie the older plains material.

A plateau, studded by the hills called Alpheus Colles, dominates the east half of the map area and is the 

western part of a broad plateau in Hellas Planitia’s interior (Leonard and Tanaka, 2001). The beds composing 

it are seen in MGS images and in the best Viking images to be finely stratified (fig. 2) but can be divided 

consistently into only three map units, lower, intermediate, and upper Alpheus plateau materials (Hpl1, Hpl2, 

Hpl3, respectively). The many strata form a bench-and-scarp topography that implies moderate coherence 

that holds up the scarps alternating with moderate erodability that creates the benches. All three map units 

and the entire plateau are bounded by irregular scarps that demonstrate postdepositional erosion. Small hills 

beyond the scarps are probably erosional outliers of once-continuous beds. Plateau materials are protected 

from erosion by the ejecta of some craters, for example the large (23 km) Hesperian-age Beloha crater 

intersected by the cross section, that may have formed between the intermediate and upper Alpheus plateau 

materials. The cross section derived from MOLA data confirms the superposition relations among the three 

plateau units but shows that parts of the intermediate unit (Hpl2) rise higher than parts of the upper unit. This 

irregular surface of the intermediate unit and the sandwiching of Beloha and its associated ejecta suggest that 

erosion cut into the intermediate layer before the upper layer was deposited; other alternations between deposition and erosion are expected within the plateau stack. Thicknesses are estimated from the elevations at 

which the mapped units intersect the surface of the cross section: approximately 350 m each for the lower and 

intermediate plateau units and less than 150 m for the preserved outcrops of the upper unit. Future imaging 

will undoubtedly reveal new details of depositional and erosional history.

Lying upon and extending beyond the lower plateau units are sinuous ridges (fig. 3) believed to consist 

of a material deposit, sinuous ridge material (unit Hsr), rather than a structural modification of other units. 

The ridges seem to have formed during or after the growth of the plateau and were later exhumed, suggesting 

an esker-like origin.

Reticulate material (unit Hr) is more regularly textured than the plateau materials and forms north-south 

bands (and one questionable circular patch) in the western map area. The unit name is derived from roughly 

rectangular or elliptical depressions separated by interconnected bounding ridges that are generally tangential 

or normal to the basin wall (figs. 4, 5). The MOLA altimetry reveals that this interesting unit varies in elevation. Where intersected by the cross section, the main exposure lies at –5.8 km elevation. Farther south, this 

unit is exposed below –6.0 km elevation. On the map, a branch of unit Hr extends northward from the main 

exposure between long 309.5° and 310° W. and continues in the subsurface—revealed by subdued traces of 

its characteristic texture—beneath a trough filled as high as –6.9 km elevation by younger plains material 

(unit Hp). The exposures at –5.8 km are higher than any plateau surface, so the reticulate material is probably 

at least partly younger than the preserved plateau beds. Less erosion also suggests this relative youth. 

However, the lower exposures and buried extensions of reticulate material are level with the lower units of 

the plateau and could be contemporaneous with them. We suggest that this unit is a marginal facies of the 

plateau strata that is now isolated from them.

The most extensive unit west of the plateau is younger plains material (unit Hp), which encroaches on 

and visibly blankets the plateau and reticulate units. The term "plains" only means level and smooth relative 

to other units; its surface is, in fact, largely wavy or bumpy. Available images do not reveal features diagnostic of origin other than the capacity to cover, but not totally obscure, subjacent topography. Elevations of the 

younger plains material along the cross section vary from –5.8 to –6.9 km.

In the southeastern map area, two units formed at the expense of the plateau and, within broad limits, in 

the same epoch as the younger plains material. The better defined unit is knobby material (unit Hk), which 

consists of small, roughly equidimensional hills scattered across a planar surface (perhaps younger plains 

material). The knobs are pieces of the plateau that were clearly created by its breakup; they may be considered extreme forms of the erosional outliers on the plateau. Wavy material (unit Hw), between the knobs and 

the plateau and between patches of knobs, is a transitional unit that appears to be less altered than the knobby 

material and may represent viscous debris flows. The loss of coherence of the plateau sediments manifested 

in the wavy and knobby materials suggests weathering of the cementing material. Knobby material lies at or 

below –6.9 km elevation, one of the lowest spots in Hellas Planitia and, therefore, on Mars.

North of the plateau in the deepest Mars depression (Smith and others, 1999), a generally planar but 

morphologically distinctive unit is characterized by closely packed, cell-like structures that are appropriately 

called honeycomb material (unit AHh; figs. 2, 6, 7). This young deposit is part of an arcuate belt 

circumferential to the plateau. The honeycomb material and an adjacent probably gradational unit, which 

lacks distinctive features and is simply called older smooth material (unit AHs), encroach on the obviously 

older plateau beds.

Another indistinct unit completes the stratigraphic column, excluding the well-understood crater materials. This randomly scattered younger smooth material (unit As), which coats both high and low landforms, 

apparently is a minor depositional product of the wind.

ICE-COVERED LAKES

Unit boundaries at consistent elevations of –3.1, –5.4, –5.8, and –6.9 km in Hellas basin, such as older 

plains material extending to –3.1, indicate deposition from lakes (Moore and Wilhelms, 2001). Deposition by 

volcanic air fall or wind presumably would scatter materials more randomly, similar to younger smooth material (unit As). The riverlike channels called Dao and Harmakhis Valles east of the map area, and smaller 

channels entering the basin are likely sources of the water. Groundwater seepage from the walls of Hellas 

basin, would also be expected in such a broad and deep catchment (Clifford, 1993).

The unit boundary at –5.8 km is particularly conspicuous (Moore and Wilhelms, 2001). At that depth, 

the sharply defined and exposed channels, Dao and Harmakhis Valles, that evidently fed sediment-laden 

water into Hellas Planitia are succeeded westward by muted, meandering forms, probably because they are 

partly buried by the sediment they deposited (Hesperian smooth plains material of Price, 1998). Similarly, 

sediments gradually obscure channels at the mouths of terrestrial streams (Kargel and Strom, 1992). Plains at 

the north and south edges of Hellas Planitia also meet the basin wall at –5.8 km (Moore and Wilhelms, 2001). 

Along the cross section, the –5.8-km elevation grazes the surface of the uppermost exposures of reticulate 

material (unit Hr) and of the overlying younger plains material (unit Hp), which resembles the smooth plains 

material deposited from Dao and Harmakhis Valles. As noted, other exposures of the reticulate and younger 

plains units lie lower than –5.8 km. The highest plateau beds lie about 350 to 1,100 m below the –5.8-km 

elevation. A water level at –5.8 km could, therefore, account for all of the sedimentation of Alpheus plateau 

and the reticulate and younger plains materials. However, the multiple layering of the plateau and the varying 

elevations of units Hr and Hp suggest episodic cycles of deposition in a regime of fluctuating water levels.

We infer from likely Martian climates that the lake surfaces froze quickly (Haberle, 1998). Morphologies 

of some geologic units probably reflect the effects of ice: (1) Plateau and knobby materials—The plateau’s 

susceptibility to erosion, indicated by benchlike topography, layers truncated by scarps, and isolated 

erosional hills, suggests sedimentary rather than volcanic composition. Because the erosion that created the 

knobby material was so pervasive, its primary mechanism was less likely to have been wind than decay of an 

icy matrix caused by sublimation or geothermal heating, although wind probably helped erode and remove 

the material. (2) Reticulate material—Location at the periphery of the Hellas Planitia stratigraphic stack, high 

elevation, and alignment of ridges parallel to the enclosing basin wall all suggest shaping by ice-marginal 

processes including sedimentation along the periphery of an ice-covered lake, reworking by large jostling 

blocks from the icy carapace, and deposition of locally reworked material (Moore and Wilhelms, 2001). (3) 

Honeycomb material—Except for their large size (a few kilometers), the distinctive cell-like pits in this unit 

have been compared to those of terrestrial kame-and-kettle terrain created by the stagnation of ice (Kargel 

and Strom, 1992). We suggest that the pits were created by the settling of ice blocks into soft lacustrine mud 

as the lake level dropped (Moore and Wilhelms, 2001); the bounding ridges represent soft mud forced up 

between the ice blocks. At a few places, this unit surface is textured with strongly angular, hectometer-sized, 

ridge-bounded polygons (fig. 7), which we interpret as casts of cracks that were on the undersurface of the 

grounding ice. Aeolian dune origins favored by Tanaka and Leonard (1995) are refuted by the high-resolution 

MGS images, which show the pit walls or septa to be complete and sharply defined by flat tops (fig. 7). Older 

smooth material seems to grade into honeycomb material and may be additional sediment from a late lake.

Formation of the sinuous ridge material may also result from the icy history of the plateau. Similar ridges 

in Argyre Planitia were attributed to a process that is responsible for forming terrestrial eskers (Kargel and 

Strom, 1992). Eskers are accumulations of sediment deposited from water flowing in tunnels in or beneath 

ice or ice-rich material (Price, 1973; Sugden and John, 1976). They survive when the enclosing ice melts or 

when the level of a subjacent lake is lowered. This origin is compatible with the location of sinuous ridge 

material in the map area, formerly sandwiched between ice-rich plateau beds that were subsequently 

removed. Braided bed morphologies revealed by high-resolution MGS images support an esker-like origin 

(fig. 3).

GEOLOGIC HISTORY

Although other interpretations are possible, we present the simplest geologic history that can be inferred 

from stratigraphic relations visible in the map area.

After Hellas basin was created by a giant impact early in the history of Mars, it began to fill with various 

deposits. The blanketing, older plains material is the earliest deposit. This and most subsequent strata of 

Hellas Planitia were deposited from lakes that filled the basin to varying elevations marked by stillstands at 

–3.1, –5.4, –5.8, and –6.9 km. These strata include multiple beds of a once-larger plateau within Hellas Planitia, a marginal facies called reticulate material, and quasi-planar deposits that decreased in volume through 

time. Reticulate material, characterized by a structure of ridges both tangential and normal to the basin wall, 

suggests reworking by the ice that we believe covered exposed water in Martian climates. Continental 

glaciers scouring the substrate while entering Hellas Planitia from the south (Kargel and Strom, 1992) would 

produce much the same features that we observe but probably not the fine grain size inferred from fine layering and remote-sensing data or the type of grooves and ridges observed by MOC images in the putative 

approach path south of the map area (Moore and Wilhelms, 2001). Massive debris flows (Tanaka and others, 

2002) would fill the basin but probably not to such regular levels.

Erosional episodes probably intervened frequently while deposition was most active. The edges of the 

plateau sediments eroded, and parts of the plateau were broken up by decay of the ice matrix to create wavy 

and knobby materials. Escaping meltwater formed esker-like deposits. Erosion apparently removed material 

from the top of the plateau, judging from the high level of parts of the probable marginal reticulate material. 

The result was an island-like plateau that was surrounded later by more water and sediment.

Small lakes filled the remaining lowest depressions, creating a honeycomblike structure as blocks from 

the ice carapace sank into muddy sediment. Older smooth material may represent additional sedimentation. 

Winds deposited some coatings on the wall of Hellas basin and, no doubt, many other places where they 

remain unmapped. The wind has certainly been an agent of erosion for all mapped units, and aeolian (and 

pyroclastic) material may have added to the load of sediment that settled out of the water. But consistent 

deposition levels around the basin preclude aeolian deposition for the bulk of the mapped units.

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Price, R.J., 1973, Glacial and fluvioglacial landforms: New York, Hafner Publishing Company, 242 p.

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.

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.

Sugden, D.E., and John, B.S., 1976, Glaciers and landscape: New York, John Wiley and Sons, Inc., 376 p.

Tanaka, K.L., and Leonard, G.L., 1995, Geology and landscape evolution of the Hellas region of Mars: 

Journal of Geophysical Research, v. 100, p. 5407–5432.

Tanaka, K.L., Kargel, J.S., MacKinnon, D.J., Hare, T.M., and Hoffman, Nick, 2002, Catastrophic erosion of 

Hellas basin rim on Mars induced by magmatic intrusion into volatile-rich rocks: Geophysical Research 

Letters, v. 29, no. 8, p. 37-1 to 37-4.

Wilhelms, D.E., 1990, Geologic mapping, in Greeley, Ronald, and Batson, R.M., eds., Planetary mapping: 

Cambridge University Press, p. 208–260.

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QUADRANGLE LOCATION

Photomosaic showing location of map area. An outline of 

1:5,000,000-scale quadrangles is provided for reference.

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360° 315° 270° 225° 180°

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Geologic Map of Part of Western Hellas Planitia, Mars

By

Jeffrey M. Moore1 and Don E. Wilhelms2

2007

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KILOMETERS

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KILOMETERS

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Figure 2. Detailed image showing stratified plateau beds (pl) bounded 

by scarp (brackets) and onlapped (arrow) by honeycomb material (h). 

Mars Orbiter Camera (MOC) narrow-angle image M10-01313, 

centered at lat 37.9° S., long 303.3° W. North at top. Illumination from 

left. Original resolution 2.9 m/pixel. MOC wide-angle context image 

M10-01314 at lower left. Image processing courtesy of Malin Space 

Science Systems.

Figure 1. Shaded-relief map of the Hellas Planitia region color-coded by elevation 

measured by the Mars Orbiter Laser Altimeter (MOLA) and binned at 1/16°. Elevation 

scale in 1-km increments, +4 km to –8 km relative to the MOLA-derived Mars datum. 

Contours at –3.1 km (red), –5.4 km (blue), –5.8 km (yellow), and –6.9 km (white) mark 

putative water stillstands (Moore and Wilhelms, 2001).

Figure 4. Detailed image showing northwest periphery of Hellas Planitia 

including reticulate material (unit Hr) and younger plains material (unit 

Hp). These Hellas Planitia deposits abut and rest on the heavily cratered 

wall and rim of the basin (u, undivided units), which is partly blanketed by 

mantling material (unit HNp; Moore and Wilhelms, 2001). Viking Orbiter 

image 620A43, centered at lat 38.1° S., long 311.3° W., orthographically 

projected. Illumination from right.

0 1 KILOMETER

Figure 3. Detailed image showing sinuous ridges interpreted to be eskers atop a plateau outlier, top 

of image. MOC narrow-angle image M19-01067, centered at lat 41.8° S., long 308.4° W. North at 

top. Illumination from left. Original resolution 5.5 m/pixel. MOC wide-angle context image M19-

01068 at lower left (compare with geologic map). Image processing courtesy of Malin Space Science 

Systems.

VERTICAL EXAGGERATION X13

ENLARGED

AREA

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N

4 0 –4 –8 KILOMETERS

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Figure 5. Detailed image showing reticulate material (Hr) perched 

at –5.8 km as seen in MOC narrow-angle image M08-03314, 

centered at 38.3° S., 310.9° W. Original resolution 4.2 m/pixel. 

North at top. Illumination from left. Ridges, outlined in sketch at 

left, may have been formed in spaces between jostling ice blocks at 

the margin of an ice-covered lake (Moore and Wilhelms, 2001). 

There is no MOC wide-angle context image for this narrow-angle 

observation. Image processing courtesy of Malin Space Science 

Systems.

0 1 KILOMETER

Figure 7 (right). High-resolution image of honeycomb material (unit AHh) 

showing individual cells with raised rims (c in sketch at left). Proposed origin is 

deformation of soft mud by settling ice blocks (Moore and Wilhelms, 2001). 

Hectometer-scale, ridge-edged polygons (p in sketch map) might be ice-crack 

casts. MOC wide-angle context image M07-05325 at lower left. MOC narrowangle image M07-05324, centered at lat 37.4° S., long 305.1° W. Original 

resolution 2.8 m/pixel. North at top. Illumination from left. Image processing 

courtesy of Malin Space Science Systems.

0 20 KILOMETERS

Figure 6. Synoptic view of north periphery of Hellas Planitia including intermediate 

Alpheus plateau material (Hpl2) and younger honeycomb material (AHh). Part of Viking 

Orbiter image 620A47, centered at lat ~35.5° S., long ~303.5° W., oblique, rectilinear 

view. North to upper right. Illumination from right.

ENLARGED

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Prepared for the

National Aeronautics and Space Administration

Scientific Investigations Map 2953

Atlas Of Mars: Western Hellas Planitia

U.S. Department of the Interior

U.S. Geological Survey

Prepared on behalf of the Planetary Geology and Geophysics 

Program, Solar System Exploration Division, Office of Space Science, 

National Aeronautics and Space Administration

Edited by Jan L. Zigler; cartography by Darlene A. Ryan

Manuscript approved for publication November 6, 2006

Descriptions of nomenclature used on map are 

listed at http://planetarynames.wr.usgs.gov/

SCALE 1:1 004 000 (1 mm = 1.004 km ) AT 300° LONGITUDE

TRANSVERSE MERCATOR PROJECTION

20 0 20 40 60 80 100 120 140 160 180 200 KILOMETERS 

 CONTOUR INTERVAL 1,000 KILOMETERS

Planetographic latitude and west longitude coordinate system

Noachian basin (Nb), crater (Nc), and plateau (Npl) materials, undivided

AREA OF

MAP