**GEOLOGIC MAP**

**OF THE**

**POLAR REGIONS**

**OF MARS**

By

Kenneth L. Tanaka and David H.Scott

1987

Prepared for the National Aeronautics and Space Administration

by

U.S. Department of the Interior, U.S. Geological Survey

> (Published in hardcopy as USGS Miscellaneous Investigations Series Map
> I--1802--C, as part of the Atlas of Mars, 1:15,000,000 Geologic
> Series. Hardcopy is available for sale from U.S. Geological Survey,
> Information Services, Box 25286, Federal Center, Denver, CO 80225)

Please direct questions or comments about the digital version to:

> Richard Kozak
>
> U.S. Geological Survey
>
> 2255 N. Gemini Drive
>
> Flagstaff, AZ 86001
>
> e-mail: rkozak@flagmail.wr.usgs.gov
>
> **DESCRIPTION OF MAP UNITS**
>
> The map units are arranged according to their occurrences and
> associations as outlined in the correlation chart. The origin and
> composition of many units are obscure or controversial, but their
> identification is based on objective descriptions of morphologic
> characteristics visible on Viking images. Many of the units and their
> type areas occur in equatorial regions (Scott and Tanaka, 1986;
> Greeley and Guest, 1987); unit symbols, names, and groupings already
> established there are used here.
>
> **NORTH POLAR REGION**
>
> **Northern plains assemblage**
>
> Materials deposited in widespread sheets on northern plains.
> Boundaries between rock units commonly not well defined, in places
> indicated by dashed contact.

ARCADIA FORMATION---Smooth, sparsely cratered; lobate fronts visible in
places. Embays all neighboring units. (Members 2, 4, and 5 (units Aa2,
Aa4, and Aa5) mapped to south, not present in map area.)
*Interpretation:* Lava flows and sediments from local sources

Aa3 Member 3---Forms isolated patches along edge of map area between
long 170° and 180°

Aa1 Member 1---Forms low-lying plains surrounding Alba and Tantalus
Fossae

Aps SMOOTH PLAINS MATERIAL---Forms two areas of smooth, sparsely
cratered plains north of crater Lyot near edge of map area (long 315° to
340°) and near knobby, undivided material at long 193°.
*Interpretation:* Probably of diverse origin, but may primarily consist
of eolian deposits

VASTITAS BOREALIS FORMATION---Subpolar plains deposits. Type areas
designated in western equatorial region (Scott and Tanaka, 1986)

Hvm Mottled member---Characterized by high-albedo crater deposits
superposed on low-albedo, smooth-plains deposits; occurs along more than
half of edge of map area; gradational with other members, particularly
with knobby member. *Interpretation:* Lava flows, possibly erupted from
fissures and small volcanoes, or alluvial or eolian deposits. Mottled
appearance due either to relatively fresh, light-colored material
exposed during impact-crater excavation or to high-albedo eolian debris
trapped within crater ejecta

Hvg Grooved member---Marked by grooves forming polygonal pattern;
polygons commonly 5 to 20 km across; small patch at lat 80° N., long 60°
in mouth of Chasma Boreale; eroded on south side. *Interpretation:*
Degraded lava flows or sediments; grooves may be lava-cooling,
periglacial, tectonic, dessication, or compaction phenomena

Hvr Ridged member---Scattered occurrences mostly in western longitudes;
gradational with knobby, mottled, and smooth members; in places embayed
by Arcadia Formation. Ridges about 1 to 2 km wide and several to tens of
kilometers long commonly form polygons 5 to 20 km across; ridge patterns
in some southern outcrops are arcuate or concentric, as at lat 56° N.,
long 173°. *Interpretation:* Degraded lava flows or sediments; ridge
pattern may be formed by intrusion of viscous lava in grooves of grooved
member or by remnants of dikes on a stripped surface; concentric ridges
may result from scarp retreat caused by periglacial or erosional
processes

Hvk Knobby member---Characterized by abundant, kilometer-size, dark,
knoblike hills spaced generally a few kilometers apart and commonly
grouped into linear chains. Occurs in broad circumpolar belt; interknob
areas gradational with mottled and ridged members. *Interpretation:*
Knobs probably small volcanoes and highly degraded remnants of highland
material (unit HNu), crater rims, and older plains material. Interknob
plains probably degraded lava flows or sediments

> **Channel-system and eolian materials**
>
> Depositional and erosional units within channels and plains, and dune
> deposits.

Ach YOUNGER CHANNEL MATERIAL---Smooth, sparsely cratered material within
part of channel along edge of map area at long 58°; channel originated
from Tempe Fossae region to south (Scott and Tanaka, 1986). Superposed
on flood-plain material and mottled and knobby members of Vastitas
Borealis Formation. *Interpretation:* Recent fluvial material

Adc CRESCENTIC DUNE MATERIAL---Forms individual and linked crescentic
dunes; individual dunes as large as several kilometers across. Occurs
along most of edge of Planum Boreum. *Interpretation:* Active barchan
dunes made up of sand-size particles consisting of mineral grains or
dust and ice aggregates. Occurrence indicates areas of moderate sand
accumulation or erosion

Adl LINEAR DUNE MATERIAL---Forms linear, ripplelike patterns of dunes in
north polar erg in Arion Planitia and near mouth of Chasma Boreum;
wavelength of ripples about 1 to 2 km. *Interpretation:* Forms
relatively stable, mature dune field; dune orientations controlled by
oscillating wind directions. Presence indicates regime of large sand
accumulations in topographic lows

Am MANTLE MATERIAL---Smooth to hummocky deposit, as much as several
hundred meters thick; surrounds most of Planum Boreale; extent of unit
may vary seasonally. Mapped only north of lat 66° N., where thick enough
to obscure features characteristic of members of Vastitas Borealis
Formation. *Interpretation:* Eolian deposits derived from seasonal frost
and dust accumulation and perhaps erosion of polar layered deposits,
polar dunes, and subpolar plains materials

Hchp FLOOD-PLAIN MATERIAL---Smooth, moderately cratered material with
longitudinal albedo streaks; occurs at edge of map area at long 60°,
adjacent to younger channel material; forms north tip of flood-plain
deposits along west edge of Acidalia Planitia; embayed by member 1 of
Arcadia Formation. *Interpretation:* Deposits from fluvial channels
south of map area (Scott and Tanaka, 1986)

> **Western volcanic assemblage**
>
> ALBA PATERA FORMATION

Hal Lower member---Forms gently sloping plateau that emerges from
Vastitas Borealis Marked by degraded lobate flow fronts and small impact
craters; displays grabens a few kilometers across and tens to hundreds
of kilometers long; embayed by member 1 of Arcadia Formation. To south,
unit covers broad region containing most of Alba and Tantalus Fossae;
north edge of region extends into map area. Previously mapped as
cratered and fractured

plains material (Dial, 1984). *Interpretation:* Older, highly degraded
lava flows originating from Alba Patera and surrounding fractures

> **Plateau and high-plains assemblage**
>
> Consists of ancient highland terrain and local tracts of younger
> deposits that stand relatively high.
>
> POLAR DEPOSITS

Api Polar ice deposits---Residual polar cap of high-albedo material
imaged in late spring and summer (Ls=92 to 154), 1977; occurs on high
surfaces of Planum Boreum, in irregular patches north of lat 70° N.
between longs 10° and 270°, and on crater floors. *Interpretation:*
Photometry and infrared thermal mapping indicate water-ice and dust
composition (Kieffer and others, 1976). Covered by CO2 frost that
extends continuously as far south as lat 65° N. during winter. Some
outlier deposits may be wind-streaked material composed mainly of ice or
frost

Apl Polar layered deposits---Form Planum Boreum and nearby mesas south
of Chasma Boreale; smooth, uncratered; moderate albedo; Planum Boreum
cut by troughs in swirl pattern; troughs expose alternating light and
dark layers tens of meters thick, some unconformable; total thickness
estimated at 4 to 6 km (Dzurisin and Blasius, 1975) or 1 to 2 km (Wu and
others, in press). Composite age of deposits uncertain.
*Interpretation:* Deposits of mixed ice and dust. Light and dark
layering caused by variation in dust-to-ice ratio; reflects long-term
climate changes. Unconformities attributed to alternating periods of
erosion and deposition that vary from place to place or to glacial
surges

Hnu UNDIVIDED MATERIAL---Forms high-standing hills and irregular mesas
several to more than 10 km across; largest exposures make up Scandia
Colles and rims of large craters nearby. Resembles knobby member of
Vastitas Borealis Formation but hills generally larger and more closely
spaced. *Interpretation:* Remnants of ancient highland material
projecting above plains; heavily eroded by mass wasting

> **SOUTH POLAR REGION**
>
> **Channel-system and eolian materials**

Am MANTLE MATERIAL---Thin, smooth, sparsely cratered material in pits of
Angusti and Sisyphi Cavi. *Interpretation:* Cover of dust deposited by
seasonal dust storms and perhaps material eroded from pit walls by mass
wasting

Ad DUNES AND DUNE-CAPPED MATERIAL---Thick, circular, steep-edged
deposits covered by complex linear dunes and dune chains; dune ridges
concentric to edges of deposits. Unit commonly occurs on north sides of
crater floors and in low areas near edge of polar layered deposits on
Terrae Sirenum and Cimmeria. *Interpretation:* Locations and complex
shapes suggest dunes composed of ice and fine material derived from
polar layered deposits; underlying deposits may consist of polar layered
material; deposited in areas of low wind strength

Hch OLDER CHANNEL MATERIAL---Smooth, longitudinally grooved deposits
within two long sinuous channels: one channel winds through Charitum
Montes and is overlain by ridged plains material in Argyre Planitia;
other channel runs along border of Malea Planum and Promethei Terra.
*Interpretation:* Channels cut by flowing water or ground-ice sapping;
deposits may include alluvial material, glacial till, or debris flows

> **Plateau and high-plains assemblage**
>
> Dominates map area; consists of rock units having moderate to high
> relief. Includes rugged, heavily cratered materials, also volcanic and
> polar deposits forming high plains.

As SLIDE MATERIAL---Lobate, high-albedo, striated, and uncratered slope
deposits extending 5 to 10 km from massifs in southern Argyre Planitia.
*Interpreta*tion: Aprons of ice and debris eroded from highland terrain;
emplaced by gelifluction, creep, or glacial flow

> POLAR DEPOSITS

Api Polar ice deposits---Form residual high-albedo feature of Martian
southern summer (Ls=348), 1977; offset from axial-pole position about
200 km south at long 45° surface striated. *Interpretation:* Water-ice
cap, usually covered by CO2 because of colder temperature relative to
north pole; striations due to relatively strong winds

Apl Polar layered deposits---Smooth, sparsely cratered, moderate-albedo
material that forms Planum Australe; in places characterized by
alternating light and dark layers tens of meters thick; complete
sequence as much as 3 km thick. Cut by curvilinear to irregular scarps
and troughs, which include Chasma Australe; underlying terrain at base
of troughs unscarred. *Interpretation:* Ice and dust deposits; albedo
layering related to ice content that, in turn, depends on climate. Some
scarps and troughs carved by prevailing wind patterns; others possibly
formed by glacial surge. Lack of etching in underlying terrain indicates
relative softness of layered material

PLATEAU SEQUENCE---Forms rough, heavily cratered to smooth, relatively
flat terrain throughout region. Subdivision of units based on relative
age and type and degree of surface modification

Hpl3 Smooth unit---On Argyre Planitia and within intercrater areas on
plateau-sequence material, forms flat, moderately cratered, smooth
plains; embays all adjacent units; flow fronts and wrinkle ridges rare.
On Malea Planum, forms irregular surfaces superposed on ridged plains
material; eroded into knobs along edges; preserved in broad low areas or
below superposed crater ejecta (as at lat 58° S., long 327°).
*Interpretation:* Lava flows from local sources or eolian deposits,
except perhaps on Malea Planum, where may be remnants of ice-rich mantle
material

Npl2 Subdued cratered unit---Forms moderately rough, uneven plains in
broad, low-lying intercrater and intracrater regions; high density of
craters 1 to 10 km across; large subdued crater rims common; small
wrinkle ridges in places; flow fronts rare. *Interpretation:* Thin
mantle of interbedded lava flows and eolian deposits

Npl1 Cratered unit---Most widespread highland rock unit; high density of
craters \>10 km in diameter, rugged surface, moderate relief; sparse
distribution of channels, fractures, and small ridges. *Interpretation:*
Materials formed during period of high impact flux; probably a mixture
of lava flows, pyroclastic material, and impact breccia

Npld Dissected unit---Similar in occurrence and appearance to cratered
unit, but highly dissected by networks of small channels.
*Interpretation:* Origin same as cratered unit; channels produced by
rain-water runoff or ground-ice sapping

Nple Etched unit---Similar to cratered unit, but marked by flat-bottomed
troughs and knobs several kilometers in size or larger; occurs in
patches in Noachis Terra and Malea Planum *Interpretation:* Cratered
unit degraded by wind erosion and removal of ground ice, perhaps induced
by local volcanic heating

Nplr Ridged unit---Forms rough, moderately to heavily cratered terrain
containing wide, long ridges and scarps; most occurrences form wide
swath along south edge of Malea Planum and Promethei Terra.
*Interpretation:* Probably interbedded volcanic rocks and impact
breccia; ridges formed by volcanism or folding and normal faulting,
perhaps along preexisting structures related to Hellas impact basin and
other ancient crustal structures

Nplh Hilly unit---Hilly facies of cratered unit, but has higher relief
due to pronounced crater rims, massifs, and fault scarps; forms rim of
Argyre impact basin (Charitum Montes) and other hilly terrain; underlies
cratered unit. *Interpretation:* Mostly rim material of Argyre impact
basin, probably uplifted crustal material and impact breccia; other
occurrences may be volcanic, tectonic, or impact-related mountains

Hr RIDGED PLAINS MATERIAL---Forms broad, planar, moderately cratered
surfaces marked by long, linear to sinuous ridges resembling those on
lunar maria; ridges commonly several kilometers wide and tens of
kilometers long. Covers most of Malea Planum and many intercrater
regions, particularly in Terrae Sirenum and Cimmeria; embays all
adjacent units except for some young smooth materials. *Interpretation:*
Extensive flows of low-viscosity lava erupted at high rates from local
sources, including fissures and Amphitrites, and Peneus Paterae

> AMPHITRITES FORMATION

Hap Patera member---On Malea Planum forms Amphitrites and Peneus
Paterae, which are characterized by circular patterns of both wrinkle
ridges and faults. Type area: Amphitrites Patera. *Interpretation:*
Material of volcanic centers and associated ring faults from which
ridged plains material was extruded

Had Dissected member---Ridged plains material deeply furrowed by sinuous
channels and gullies that trend downslope toward Hellas Planitia
(centered at lat 45° S., long 290°); many superposed and embayed impact
craters. Forms plains of northern Malea Planum; gradational with ridged
plains material; embays rim material of Hellas Basin. Type area:
northern Malea Planum. *Interpretation:* Relatively soft ridged plains
material or mantle modified by channeling

DORSA ARGENTEA FORMATION---Forms polar plains near Angusti and Sisyphi
Cavi and Promethei Rupes; embays older highland rocks and ridged plains
material; underlies polar layered deposits; middle Hesperian age
indicated by crater counts

Hdu Upper member---Deposits generally broad and smooth, lightly pitted
in places, except at Dorsa Argentea, where deposits have sinuous,
braided, kilometer-wide ridges as long as 150 km. Edges locally distinct
and lobate; embays surrounding cratered terrain. Type area: Dorsa
Argentea. *Interpretation:* Lava flows originating from unrecognized
fissure vents in vicinity of crater Schmidt, Sisyphi Montes, and other
local sources; ridges may be unusual lava-flow features or eskers

Hdl Lower member---Similar to upper member but more degraded; forms
mostly smooth pitted plains around cavi. Type area: plains surrounding
Angusti and Sisyphi Cavi. *Interpretation:* Eolian mantle or lava flows
originating from local fractures and possible volcano at Sisyphi Cavi.
Highly degraded by cavi formation, perhaps facilitated by removal of
underlying ground ice

HELLAS ASSEMBLAGE---Map units associated with impact and fill of Hellas
impact basin (Greeley and Guest, 1987). Only one of these units is
exposed in south polar map area

Nh1 Basin-rim unit---Rugged to mountainous, heavily cratered and
resurfaced material of Hellas Basin rim east of Malea Planum.
*Interpretation:* Impact breccia and interbedded volcanic material of
ancient crust; impact structures such as radial troughs not seen,
probably degraded and buried by surficial deposits

Nhu UNDIVIDED MATERIAL---Rough, massive deposits exposed in walls and
floors of large, irregular pits as much as a kilometer deep at Angusti
and Sisyphi Cavi; forms closely spaced, rounded hills a few kilometers
across; grades into etched unit of plateau sequence. Most of unit
underlies Dorsa Argentea Formation. *Interpretation:* Plateau sequence
and basement rocks; pitting and degradation caused by removal of ground
ice, mass wasting, and eolian exhumation of poorly consolidated material

CONTACT Dashed where approximately located or gradational; queried where
doubtful

FAULT OR GRABEN---Bar and ball on downthrown side of fault

RIDGE---Symbol on ridge crest

SCARP---Line marks top of slope; barb points downslope

NARROW CHANNEL

CALDERA

DOME---Low, moderately sloping; origin and age uncertain

MOUNTAIN---High, rugged; origin and age uncertain

VOLCANO---Queried if origin conjectural; age uncertain

IMPACT CRATER MATERIALS---Yellow if superposed, brown if partly buried.
May include rim crest (hachured), central peak, smooth floor (symbol s).
Symbol c denotes crater-rim and ejecta materials. Materials of impact
craters less than about 100 km across not mapped. Ejecta from crater
Lyot, centered at lat 50° N., long 331°, shown by symbol el.

**INTRODUCTION**

These geologic maps of the north and south polar regions of Mars,
extending to 55° north and south latitudes, overlap by 2° the geologic
maps of the western and eastern regions, which extend to lat ±57°. The
maps were compiled from Viking medium-resolution photomosaics at scales
of 1 :2,000,000 and from higher resolution Viking images. The quality
and resolution of the Viking pictures are superior to those of Mariner 9
used to prepare the previous map (Scott and Carr, 1978) that includes
these two regions. Because of the Viking orbital configuration, a vast
number of high-resolution images of the area within 10° of the north
pole was obtained, whereas many areas in lower northern latitudes were
covered only by low-resolution images. In contrast, the south polar
region is nearly completely covered by images at medium resolution but
is not imaged at high resolution.

Names of geologic units and a method for relative-age determinations
based on crater densities were developed for the geologic map of the
western equatorial region (Scott and Tanaka, 1986). These names, where
applicable, and this dating method were also used on these polar maps.
New geographic nomenclature and several new geologic units were added.

The Mariner 9-based map of the north polar region (Scott and Carr, 1978)
indicates mottled, ridged, and cratered plains surrounding the polar
deposits. Recent mapping at 1:5,000,000 scale and crater counts above
lat 65° N. by Dial (1984), based largely on Viking images, have outlined
the vast sand seas that surround the north polar ice cap, changed the
age of the plains of Vastitas Borealis from Noachian-Amazonian to
Amazonian-Hesperian, identified faulted terrain associated with Alba
Patera, and reclassified as impact craters three structures previously
identified as volcanoes. Dial subdivided the plains units largely on the
basis of albedo, mantling by debris, and presence of fractures, but only
Mariner 9 frames were available to him for much of the plains. Our
mapping covered 10° more of latitude and used new Viking-based
1:2,000,000-scale photomosaics (resolution ranges from 150 to 400
m/pixel) that fully cover these plains, as well as high-resolution
images of the polar ice cap. We subdivided the northern plains
materials, excluding relatively thin eolian deposits, into six members
of the Vastitas Borealis and Arcadia Formations (Scott and Tanaka,
1986).

Our south polar map was based on Viking 1:2,000,000-scale photomosaics
made up mostly of images ranging in resolution from about 130 to 200
m/pixel. Highest resolution images are about 110 m/pixel. Some areas,
particularly those within the arc between lat 55° and 60° S. and long 0°
and 180°, are covered only by lower resolution images (200 to 400
m/pixel). Previous mapping at 1:5,000,000 scale south of lat 65° S.
(Condit and Soderblom, 1978), based on Mariner 9 images (300 to 3,000
m/pixel), identified the extent of the polar deposits, the rugged
character of the highlands, and large areas of relatively smooth plains.
Important modifications in the new south polar map include the
following: (1) a finer subdivision of highland units but without major
changes in their relative-age assignments; (2) an extension of the area
covered by ridged plains material from a relatively small area to many
areas surrounding the south pole; and (3) the inclusion of the Hesperian
Dorsa Argentea and Amphitrites Formations, consisting of four units.

The north and south polar regions are strikingly different in
physiography, geology, relative age, and surface processes. Most of the
differences reflect the contrast between younger lowland plains of the
northern hemisphere and older highland terrains of the southern. The
northern plains consist of comparatively few rock types that are mostly
of Hesperian and Amazonian age. After their emplacement, chiefly as lava
flows and sediments, the plains-forming units were extensively mantled
and stripped (Carr and Schaber, 1977). These older units now exist only
as numerous small knobby hills and pedestal craters throughout the
region. Some scattered clusters of larger hills that form Scandia
Colles, for example, may be remnants of an old highland surface that
projected above the later lava flows of the plains. The plains north of
about lat 65° N. are mostly

covered by dune fields, dust mantles, and polar layered deposits that
form Planum Boreum and some outlying mesas. The extensive residual
water-ice cap around the north pole covers most of the layered deposits.
In contrast, the rock units of the south polar region are continuations
of many highland units of Noachian and Hesperian age that are exposed
throughout the equatorial zone. These rocks are overlain south of about
lat 70° S. by Planum Australe, a broad, smooth structure composed of
layered deposits and a small residual ice cap. Relatively little dune
and mantle material surrounds these deposits. The contrasting characters
of the polar highlands and lowlands are probably manifestations of
different crustal thicknesses of highland and lowland terrain (Bills and
Ferrari, 1978) and, therefore, of early global crustal evolution.

Isolated volcanoes, mountains, and domes are scattered throughout the
map areas, but as a group they are not assigned a position in the
stratigraphic column because the small size of the features precludes
reliable crater counts on an individual basis. The stratigraphic
relation between low domes (symbol d) and surrounding plains in the
north polar region is uncertain. Some mountains in the south polar
region are younger and some older than surrounding units. Mountains
having features interpreted to be volcanic, such as summit depressions
and flow patterns on their flanks and around their bases, are shown in
red and are designated by the symbol v. Others may be degraded
volcanoes, tectonic mountains, and remnants of plateau sequence
materials; these are shown in gray and are designated by the symbol m.

**NORTH POLAR REGION**

> **Physiographic setting**

The north polar region of Mars consists largely of broad, flat plains
surrounding Planum Boreum, a subcircular plateau 1,100 to 1,200 km in
diameter centered near lat 87° N., long 0°. The height of the plateau is
uncertain; low-resolution stereoimaging of Mariner 9 pictures suggests
about 4 to 6 km of relief (Dzurisin and Blasius, 1975), and similar work
on Viking images suggests about 1 to 2 km of relief (Wu and others, in
press). The plateau is dissected by long, arcuate troughs that form a
counterclockwise swirl pattern extending outward from the pole. Depths
of these troughs range from 200 to 800 m (Blasius and others, 1982).
Outlying remnants of the plateau form an annular belt of mesas partly
encircling it between lat 75° to 80° N. and long 100° to 270°. Near the
mouth of Chasma Boreale, these mesas are several hundred kilometers from
the plateau. Lower latitude areas of the north polar plains are
interrupted by knob-shaped highland remnants that make up Scandia Colles
and by scattered impact craters as large as 140 km in diameter. A belt
of linear dunes forms the broad, arcuate Olympia Planitia adjacent to
Planum Boreum between long 120° and 240°

> **Stratigraphy and structure**

The oldest rocks in the map area are *undivided material* (unit HNu).
Its most widespread outcrops form the knobby hills of Scandia Colles,
which are interpreted to be remnants of ancient cratered terrain (Morris
and Howard, 1981). Although their surfaces are too degraded for
meaningful crater-density determinations, the hills are considered
Noachian-Hesperian in age because they include a crater 150 km in
diameter that resembles craters of Noachian age in the cratered terrain
of the equatorial and south polar regions, and because the hills are
embayed by upper Hesperian plains material. They are likely to be
similar in composition to the plateau sequence (highland rocks), which
probably consists of interbedded impact breccia and lava flows, in the
equatorial and south polar regions. Erosion of the early heavily
cratered terrain materials probably occurred during late Noachian time
and continued during Hesperian time, as evidenced by stripping of upper
Hesperian plains materials that had embayed the older highland remnants.

Early in the Hesperian Period, lavas of the *lower member* (unit Hal) of
the *Alba Patera Formation* flowed northward beyond lat 60° N., where
they were moderately fractured by the late Hesperian, northeast-trending
faults of Alba and Tantalus Fossae. Also during the late Hesperian, the
north tip of an extensive deposit of *flood-plain material* (unit Hchp)
was emplaced along the west edge of Acidalia Planitia (Scott and Tanaka,
1986).

Much of the north polar plains is covered by materials of the Vastitas
Borealis Formation. Cumulative densities of craters larger than 5 km in
diameter indicate that the formation is middle to late Hesperian in age,
which agrees with counts by Dial (1984). The formation is divided into
four members on the basis of the generally mutually exclusive dominance
of knobs, grooves, ridges, and mottling, although at many places the
members are gradational. The small, kilometer-size hills that
characterize the *knobby member* (unit Hvk) were interpreted as small
volcanoes or highly degraded remnants of highland material (Frey and
others, 1979; Scott, 1979). Interknob surfaces are commonly grooved,
ridged, mottled, or mantled. This unit was mapped as both mottled and
mantled cratered plains material in the north polar area (Dial, 1984)
and as hummocky mottled plains material and knobby plains material in
the northern part of the Mare Acidalium quadrangle (Witbeck and
Underwood, 1984) . The *grooved member* (unit Hvg) is characterized by a
pattern of grooves that form polygons generally 5 to 20 km across; the
member is clearly exposed at the mouth of Chasma Boreale but may be
covered by mantle material elsewhere. Dial (1984) assigned a lower
Amazonian age to this exposure. The origin of the grooves has been
attributed to ice wedging, ground-ice decay, thermal contraction of lava
flows, dessication, tectonism, or compaction (Carr and Schaber, 1977;
Scott, 1979; Helfenstein

and Mouginis-Mark, 1980; Pechmann, 1980; McGill, 1985). The *ridged
member* (unit Hvr) consists of ridges 1 to 2 km wide forming two
distinct pattern types: (l) arcuate, locally concentric patterns
possibly formed by retreat of a debris and ice mantle (Carr and Schaber,
1977) or by subsurface ice removal from plains material (Guest and
others, 1977); and (2) polygonal patterns that appear similar in size
and shape to those of the grooved member; the ridges locally grade into
grooves. Pechmann (1980) proposed that the ridges are either the result
of high-viscosity lavas extruded through the grooves or the remnants of
resistant materials, emplaced in former grooves, which now protrude
after stripping of interridge areas. Alternatively, the ridges may be
subglacial volcanic deposits (moberg ridges). The *mottled member* (unit
Hvm) consists of bright splotches of impact-crater ejecta superposed on
both smooth and patterned dark plains material. The contrast in albedo
may be caused by eolian material trapped on rougher crater surfaces or
by light-colored subsurface material excavated by impact craters
(Soderblom and others, 1973b; Carr, 1981). This unit makes up most of
the area between lat 55° to 60° N. and long 175° to 60°. Formerly, the
mottled member was mapped more extensively in the north polar plains and
was not distinguished from other members of the formation (Soderblom and
others, 1973b; Dial, 1984). The members of the Vastitas Borealis
Formation are overlain by layered and mantle material near the pole, but
where they can be identified beneath the mantle, they are shown by
symbol in parentheses. Some low domes as large as 50 km in diameter that
protrude through the mantle material near lat 75° N., long 155° may be
viscous lava flows or volcanoes that were source vents for some of the
surrounding plains materials. The general composition of the Vastitas
Borealis Formation is uncertain; possible origins include lava flows and
alluvial and eolian sediments (Carr and Schaber, 1977; McGill, 1985).

Early in the Amazonian Period, plains material of *member 1* (unit Aa1)
of the Arcadia Formation flooded and embayed the northern periphery of
the Alba Patera lava flows and members of the Vastitas Borealis
Formation. *Smooth plains material* (unit Aps) was deposited as well,
principally north of crater Lyot. In the middle Amazonian, small patches
of *member 3* (unit Aa3) *of the Arcadia Formation* were emplaced at lat
55° N. between long 170° and 180°. North of Tempe Fossae, *younger
channel material* (unit Ach) was deposited on older floodplain material
and members of the Vastitas Borealis Formation.

The *polar layered deposits* (unit Ap1) also overlie the Vastitas
Borealis Formation. These deposits have been described extensively by
other workers, including Blasius and others (1982) and Howard and others
(1982). They make up Planum Boreum and are exposed within troughs that
form its swirl pattern. The deposits consist of a series of alternating
light and dark layers, each a few tens of meters thick, that are
continuous for hundreds of kilometers. Thinner beds may be present but
are not resolvable in available images. The deposits probably consist of
water ice and dust (Kieffer and others, 1976), which probably is
transported poleward by wind storms and is contained in CO2-ice
particles deposited on the poles during winter (Cutts, 1973). Dust
accumulation at present on the north polar layered terrain is estimated
to be about 4x10-2 cm/yr (Pollack and others, 1979). The alternation of
layers may reflect changes in the ice-to-dust ratio, which are possibly
a result of climatic oscillations caused by rotational and orbital
perturbations having characteristic periods of 51,000 to 2,000,000 years
(Cutts and others, 1979; Carr, 1982). Eroded outliers of layered
materials, and possibly the unconformities in the layered sequences
(Cutts and others, 1976), indicate past, and possibly continuing,
erosion of parts of the deposits by eolian and insolation processes. The
paucity of impact craters on the layered deposits suggests surface ages
of no more than a few tens of million years (Carr, 1982), but the age of
the deposits themselves is uncertain because they may be periodically
reworked by rotational migration of the large chasmata and troughs
(Howard, 1978; Cutts and others, 1979). Alternatively, these large
spiral valleys and the unconformities in the valley walls may have
resulted from glacial surges partly directed by Coriolis forces
(Weijermars, 1986).

The residual *polar ice deposits* (unit Api) of late Martian spring and
summer were mapped from medium-resolution photomosaics. The residual ice
cap occurs mainly on the plateau surface of the polar layered deposits
and in low areas (such as crater floors) north of about lat 70° N.
Although it is overlain by a winter cap of solid CO2, Viking thermal and
reflectance data show that the residual north polar cap is composed of
water ice and dust (Kieffer and others, 1976). Even the smaller ice
patches are relatively stable on the short term because only small
amounts of water ice sublime during the summer; however, long-term
climatic variations would alter their distribution pattern. The center
of the cap is displaced nearly 200 km to the south of the axial-pole
position at long 0°, away from extensive linear dune and mantle
deposits; this displacement may be a result of prevailing wind patterns.

Extensive dune deposits surround the north pole. They are probably
composed of sand-size mineral grains and bonded aggregates (Sagan and
others, 1977; Greeley and others, 1982). Dune patterns (Breed and
others, 1979) and volumetric considerations (Thomas, 1982) suggest that
these particles are eroded from the polar layered deposits. Both the
layered deposits and the dune sand may have been derived from fluvial
deposits (McCauley and others, 1980) or other erosional debris (Tsoar
and others, 1979) from the middle and upper northern latitudes. Patches
of *crescentic dune material* (unit Adc) surround most of the pole
between lat 75° and 80° N. *Linear dune material* (unit Adl), which
forms a finely rippled topography seen on high-resolution images, occurs
mostly adjacent to polar layered deposits in Olympia Planitia and near
the mouth of Chasma Boreale. The linear dunes indicate a large sand
supply deposited in a topographic basin over a long period of time,
whereas the crescentic dunes form where sand supply is smaller and more
transient (Breed and others, 1979).

Surrounding the pole, *mantle material* (unit Am) consists of surficial
deposits generally less than 200 m (Squyres, 1979) or 600 m (Botts,
1980) thick that subdue and bury topographic and albedo features on the
underlying plains materials. The mantle was initially identified as
burial and infilling material of impact craters and was interpreted to
consist of eolian dust (Soderblom and others, 1973a), perhaps deposited
similarly to the polar layered deposits but on an ice-free surface
(Squyres, 1979). The mantle covers large areas as far south as lat 30°
N. (Soderblom and others, 1973a, 1973b; Dial, 1984).

**SOUTH POLAR REGION**

> **Physiographic setting**

The south polar region of Mars consists largely of highland terrain
rising several kilometers above the Martian datum. Elevations were
obtained from Mariner 9 radio occultation and ultraviolet spectrometer
data (Dzurisin and Blasius, 1975) and Viking photogrammetrically derived
topographic maps (Wu and others, in press). The south pole is capped by
a plateau of polar layered deposits, Planum Australe, whose relief is
generally 2 to 3 km but more than 5 km where it is covered by polar ice
deposits. Planum Australe is oblong in plan, about 1,600 km long and
1,200 km wide, and is offset about 300 km from the geographic pole along
the prime meridian. The surface of this plateau slopes downward into an
850-km-diameter impact basin whose rim is partly outlined by Promethei
Rupes (Wilhelms, 1973). Along the edge of the map area lie rugged
terrains of the Argyre and Hellas impact-basin rims. Many impact craters
exceeding 100 km in diameter occur in the highland terrain surrounding
Planum Australe. The south polar region also includes two areas of
steep-sided depressions several hundred kilometers across, Angusti and
Sisyphi Cavi, which contain pits more than 1 km deep.

> **Stratigraphy and structure**

One of the two oldest materials exposed in the south polar region is the
*basin-rim unit* (unit Nh1) of the *Hellas assemblage* (Greeley and
Guest, 1987), which forms the rim of the Hellas impact basin. This unit
is rugged and heavily cratered, probably composed of impact ejecta and
faulted crustal material (Potter, 1976; De Hon, 1977; Peterson, 1977).
On the southeast side of Hellas Planitia, the basin-rim unit extends as
far as 1,800 km from the basin rim, but, on the west side, it extends
for only 200 to 300 km (Peterson, 1977). Possibly this asymmetry is due
to ejecta from some smaller impact craters on the east side of Hellas
Planitia (Potter, 1976), extensive resurfacing of the western rim area,
or the obliquity of the Hellas impact that may have preferentially
distributed ejecta to the southeast.

In contrast, the other early Noachian material, the *hilly unit* (unit
Nplh) of the plateau sequence, is more uniformly distributed (Scott and
Carr, 1978). It is rugged and locally faulted; in addition to making up
the rim of the Argyre impact basin, it forms isolated mountains of
possible volcanic or tectonic origin. The hilly unit is embayed by the
*cratered unit* (unit Npl1) of the plateau sequence. This unit forms
most of the basal rocks throughout the map area. It was produced during
the early period of heavy bombardment and is interpreted to consist of
interbedded impact breccia and lava flows. In some areas, the cratered
unit was extensively dissected by subparallel sets of small narrow
channels; these areas are mapped as the *dissected unit* (unit Npld).
The channels resemble those produced by terrestrial streams and have
been attributed to runoff of rain water (Masursky and others, 1977) or
ground-water seepage (Pieri. 1980, p. 148) during a period when
atmospheric conditions may have allowed liquid water at the surface. The
*etched unit* (unit Nple) consists of etched and knobby components of
the cratered unit. Its surfaces were probably formed by sublimation of
ground ice, perhaps instigated by local volcanic heating, and deflation
of the material.

During middle to late Noachian time, systems of large linear ridges
formed on the cratered unit. They are similar to lunar mare and Martian
wrinkle ridges in shape and possibly in origin, but generally are larger
and occur on older, more rugged surfaces. Material containing the ridges
is mapped as the *ridged unit* (unit Nplr) of the plateau sequence. It
mostly lies within a swath several hundred kilometers wide that extends
across the map area between long 190° and 340° and includes the scarps
and ridges that make up Chalcoporos Rupes, Pityusa Rupes, Dorsa Brevia,
and Thyles Rupes. Most of these ridges are parallel with the swath. West
of long 270°, they appear to be part of a concentric band around Hellas
Planitia that includes scarps and troughs 2,000 to 3,000 km west of the

center of the low plain (Peterson, 1977). The ridges may be part of a
ring system or a result of rejuvenation of older basin structures;
possibly they include volcanic material erupted contemporaneously with
the structural deformation. East of long 270°, the ridges deviate from
their patterns concentric to Hellas and follow trends parallel to local
northeast-trending wrinkle ridges. Orientation of the unit\'s ridges may
be controlled by an ancient lineament system defined by the
Elysium-Amphitrites and the Tharsis Montes volcanic loci, by deformation
produced by an oblique impact at the Hellas basin, or both.

During the later part of the Noachian Period, many intercrater and
intracrater areas were covered by a thin mantle of probable volcanic and
eolian origin, which embayed but did not completely bury most craters
larger than tens of kilometers in diameter. The mantle is mapped as the
*subdued cratered unit* (unit Npl2). At places in the unit are lava-flow
scarps and small ridges and channels.

The *smooth unit* (unit Hpl3) of the plateau sequence has two facies.
One form is at Argyre Planitia and within intercrater areas on
plateau-sequence material, where it is fairly smooth and moderately
cratered. Stratigraphic relations for these outcrops generally indicate
a lower to middle Hesperian age. The second form is superposed on ridged
plains material in low areas, beneath the ejecta of larger craters, and
has steep, irregular, and locally knobby edges indicating extensive
erosion. The favored preservation of the unit beneath crater ejecta
probably is due to armoring, as proposed for the pedestals of craters in
the north polar plains (McCauley, 1973). Although designated Hesperian
in age and at least moderately cratered, these outcrops of the smooth
unit are not well constrained stratigraphically, and some may be
Amazonian in age. Possibly they represent remnants of mantle material
similar to the thick, extensive blanket around the north pole.

Other resurfacing of intercrater areas and the southern rim of Hellas
impact basin took place during early Hesperian time, forming principally
the *ridged plains material* (unit Hr). This unit is characterized by
wrinkle ridges generally a few kilometers wide and tens of kilometers
long. They have been interpreted as lava flows (Greeley and Spudis,
1981) erupted from buried fissures and large calderas. On Malea Planum,
ridged plains material appears to have been erupted from Amphitrites and
Peneus Paterae. The ridged plains material within them constitutes the
*patera member* (unit Hap) *of the Amphitrites Formation*. The paterae
are interpreted to be circular volcanic centers characterized by
concentric and radial wrinkle ridges and, at Amphitrites and Peneus
Paterae, by ring faults. North of these ring-faulted paterae the ridged
plains material is deeply dissected and furrowed (Potter, 1976), and it
is mapped as the *dissected member* (unit Had) of the Amphitrites
Formation. This unit forms a broad shield and may consist of pyroclastic
material or relatively erodable lava flows similar to material on the
flanks of Tyrrhena and Hadriaca Paterae northeast of the Hellas impact
basin (Greeley and Spudis, 1981).

Two distinctive sequences of smooth, pitted plains material having flow
fronts and braided ridges characterize the *Dorsa Argentea Formation*.
The flow fronts were not apparent on Mariner 9 images, and the material
was interpreted as eolian dust and ice (Condit and Soderblom, 1978).
Flow fronts are recognizable south of Promethei Rupes, surrounding
Sisyphi Montes, and in Aonia Terra, northeast of crater Schmidt. The
material in other areas is pitted but otherwise featureless, and it may
be better described as a massive blanket. The two sequences are mapped
as upper and lower units on the basis of stratigraphic position and
degree of degradation. Most of the *lower member* (unit Hdl) of the
Dorsa Argentea Formation occurs within and around Angusti and Sisyphi
Cavi; it appears to have been erupted from local fissures, now buried,
and from an apparent volcano with a summit crater. The *upper member*
(unit Hdu) is more widespread to the east and south, filling low
intercrater areas and part of the basin bounded by Promethei Rupes. Its
flows also may have issued from buried fissures and possible dome-shaped
volcanoes (mapped as mountains). Although generally smoother than the
lower member, the upper member has many sinuous, braided ridges of
uncertain origin that follow the flow direction of the lavas. Deposits
bearing similar ridges in southern Argyre Planitia have been mapped as
ridged plains material. Howard (1981) suggested that the ridges may be
eskers;

however, supporting stratigraphic relations within the cavi terrain and
geologic evidence (for example, fan deposits and glacial features) are
lacking. Alternatively, the ridges may be a type of lava-flow feature
formed under unusual conditions.

The Dorsa Argentea Formation is deeply pitted and etched at Angusti and
Sisyphi Cavi, exposing generally older *undivided material* (unit HNu).
This material is composed of plateausequence and other old materials
(which are divided according to surface characteristics).

Much of the highland surface adjacent to or surrounded by the upper
member of the Dorsa Argentea Formation in the Sisyphi Cavi and Montes
region is pitted or knobby (mapped as units HNu and Nple). Originally,
Cutts ( 1973) and Sharp ( 1973) proposed that wind erosion of ice-rich
material caused the pitting, because the adjacent polar layered deposits
are etched by the wind. Condit and Soderblom (1978) suggested that the
pits were formed by eolian erosion of soft materials that bury the
cratered terrain. However, Viking images reveal that the pits are deep
(about 1 km) and were excavated through the Dorsa Argentea Formation
into the underlying rocks. Howard (1981) suggested that basal melting of
ground ice could have formed the cavi, an interpretation consistent with
a geologic history in which volcanic activity associated with the lower
member of the Dorsa Argentea caused ground-ice melting; such melting
could have aided formation of the deeply pitted terrain generally south
of lat 75° S. and the etched and knobby terrain to the north. After
emplacement of the upper member, minor pitting and degradation
continued, particularly in areas already pitted. Channels cutting
Charitum Montes and the east edge of Malea Planum deposited *older
channel material* (unit Hch), probably also in Hesperian time.

During the Amazonian Period, volcanism and tectonism decreased, and
surficial eolian deposits and debris aprons were formed. The *polar
layered deposits* (unitApl) are estimated to be either 1 to 2 km thick
(Dzurisin and Blasius, 1974) or 2 to 3 km thick (based on maps by Wu and
others, in press). They probably consist of interlayered eolian dust and
ice (Sharp, 1973). The margins of the deposits, particularly between
long 140° and 270°, are relatively thin, and crater rims of the
underlying terrain are exposed. The south polar layered deposits are
similar in form to their counterparts in the north polar region. In
addition, they show long, gently curving scarps etched into the margins
of Chasma Australe and other troughs (Cutts, 1973; Thomas, 1982). These
scarps, along with the present global dust-storm patterns and the
scarcity of surrounding mantle deposits, suggest that the south polar
layered deposits are presently being eroded and transported to the north
polar region (Scott and Tanaka, 1985). The etched scarps are parallel to
the 60° to 90° meridians and appear superposed on a possibly clockwise,
spiral pattern of subdued troughs, cutting the troughs at oblique
angles. The clockwise spiral pattern indicates the troughs were produced
by glacial surge, not by polar winds, on the basis of directional
patterns predicted from guidance by the Coriolis effect for each of the
processes (Weijermars, 1986). Although the history of the south polar
layered deposits is generally uncertain, the fact that a few craters are
superposed on them indicates that their surfaces, on average, are older
than surfaces of the north polar deposits. The extent of the residual
*polar ice deposits* (unit Api), mapped during the Martian southern
summer of 1977, is slightly greater than that observed by Mariner 9,
perhaps because of retarded ice-cap retreat due to a global dust storm
(James and others, 1979). Unlike the north polar cap, the residual south
polar ice cap is usually covered by CO2 year round, but it may
occasionally expose water ice during years of high retreat (Jakosky and
Barker, 1984).

Relatively recent eolian sedimentation has produced dunes and
*dune-capped material* (unit Ad). Dunes cover thick deposits on low
plains and within craters outside the periphery of the polar layered
deposits; the thick deposits may themselves be remnants of the layered
deposits. Mass wasting and dust deposition are evidenced by *mantle
material* (unit Am) that fills some pits in Angusti and Sisyphi Cavi and
by *slide material* (unit As) surrounding massifs in southern Argyre
Planitia. The slides may be aprons composed of eroded debris and ice
that flow by gelifluction and frost creep (Carr and Schaber, 1977) or
ice creep (Squyres, 1978).

**THE MARTIAN POLAR DICHOTOMY**

The lowlands and highlands of the north and south polar regions of Mars
contrast in physiography, geology, and geophysics. The average elevation
of the north polar plains is generally at or below the Martian datum,
whereas the south polar highlands surface is about 2 to 4 km above datum
(Wu and others, in press). The highland-lowland transition zone is
typified by a scarp hundreds of meters to more than a kilometer high;
elsewhere it is commonly composed of isolated mesas and knoblike
remnants of the highlands extending northward into the plains. Surfaces
south of the scarp (including those of the south polar region) are
dominated by rugged, heavily cratered terrain. To the north, the surface
is relatively smooth except for local patches of knobby remnants of
heavily cratered terrain (for example, Scandia Colles). Ancient terrain
in the northern lowlands was mostly buried by lava flows or sediments
(Scott and Carr, 1978; McGill, 1985), some of which originated in the
highlands (Scott and Tanaka, 1986). Geophysical models for the isostatic
state of Martian topography suggest that the northern plains low is
partly to entirely compensated (Phillips and Saunders, 1975) and
underlain by a relatively thin crust (Bills and Ferrari, 1978).

The origin of the northern plains topographic low is uncertain.
Suggestions include (1) crustal disruption caused by an increase in
mantle volume due to a phase change (Mutch and Saunders, 1976), (2)
crustal collapse produced by mantle convection and upwelling due to core
segregation (Wise and others, 1979), and (3) massive excavation caused
by a giant impact event (Wilhelms and Squyres, 1984) or many large
impacts (Frey and others, 1986). Each of these explanations can account
for the depth and roughly circular outline of the northern lowlands. The
rocks of the northern lowlands are relatively young and obscure possible
underlying structures. The highland-lowland transition zone apparently
has eroded back hundreds of kilometers, and no broad structural pattern
in the highlands relative to the lowlands has been demonstrated.
Although gravity models from Viking spacecraft-tracking data may yield
some further insights into the highland-lowland boundary problem, those
data are relatively poor because spacecraft altitude was high and
tracking geometry in the high latitudes was indirect. Thus, the origin
of the northern lowlands will remain undetermined until future missions
to Mars supply us with new data.

**ACKNOWLEDGMENTS**

We thank Michael H. Carr of the U.S. Geological Survey and Ronald
Greeley, Eileen Theilig, and Edward F. Albin of Arizona State University
for thoughtful and prompt reviews of the map and text. Marlene Tuesink
of the U.S. Geological Survey counted craters for many of our geologic
units.

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**NOTES ON BASE**

This map sheet is one of a series covering the entire surface of Mars at
a scale of 1:15,000,000. Sources for the map base were 1:5,000,000-scale
shaded relief maps described by Batson and others (1979). Data used in
the map portrayal were obtained from Viking Orbiter images.

ADOPTED FIGURE

The figure of Mars used for computing the map projections is an oblate
spheroid (flattening of 1/192) with an equatorial radius of 3,393.4 km
and a polar radius of 3,375.7 km.

PROJECTIONS

The Mercator projection is used between the 57° parallels; the Polar
Stereographic projection is used for the polar regions north and south
of the 55° parallels. Scales are 1:15,000,000 at the equator and
1:9,203,425 at the poles. The projections have a common scale of
1:8,418,000 at lat ±56°. Longitude increases to the west in accordance
with astronomical convention for Mars. Latitudes are areographic.

CONTROL

Planimetric control for the 1:5,000,000-scale maps used to compile the
bases for these sheets was derived from photogrammetric triangulations
by use of Mariner 9 pictures (Davies, 1973). This control net was
upgraded through the use of Viking data (Davies and others, 1978). At
least 85 percent of the image control points lie within 0.5 mm of the
positions published in 1978.

MAPPING TECHNIQUE

The mapping bases for this series were assembled from 1:5,000,000-scale
shaded relief maps reduced and digitally transformed where necessary to
fit the projections. During shaded relief portrayal, features on these
bases were used to position details taken from Viking Orbiter pictures.
Features were drawn as if illuminated uniformly from the west, through
use of airbrush techniques described by Inge (1972) and
photointerpretive methods described by Inge and Bridges (1976). The
shading is not generalized and accurately represents the character of
surface features.

Shaded relief analysis and portrayal were made by Barbara J. Hall (south
pole) and Jay L. Inge (north pole).

NOMENCLATURE

All names on this sheet are approved by the International Astronomical
Union (IAU, 1974, 1977, 1980, 1983, and 1986). Named features and their
positions are taken from published maps of Mars that have scales of
1:2,000,000, 1:5,000,000 and 1:25,000,000.

M 15M±90/0 G Abbreviation for Mars; 1:15,000,000 series; center of maps,
lat 90° N. or lat 90° S., long 0°; geologic map (G).

REFERENCES

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.

Davies, M.E., 1973, Mariner 9: Primary control net: Photogrammetric
Engineering, v. 39, no. 12, p. 1297--1302.

Davies, M.E., Katayama, F.Y., and Roth, J.A., 1978, Control net of Mars:
February 1978: The Rand Corporation, R-2309-NASA, 91 p.

Inge, J.L., 1972, Principles of lunar illustration: Aeronautical Chart
and Information Center Reference Publication 72-1, 60 p.

Inge, J.L., and Bridges, P.M., 1976, Applied photointerpretation for
airbrush cartography: Photogrammetric Engineering and Remote Sensing, v.
42, no. 6, p. 749--760.

International Astronomical Union, 1974, Commission 16: Physical study of
planets and satellites, and Lunar and martian nomenclature, *in* 15th
General Assembly, Sydney, 1973, Proceedings: International Astronomical
Union Transactions, v. 15B, p. 105--108, 217--221.

\_\_\_\_\_\_\_1977, Working Group for Planetary System Nomenclature,
*in* 16th General Assembly, Grenoble, 1976, Proceedings: International
Astronomical Union Transactions, v. 16B, p. 321--325, 331--336,
355--362.

\_\_\_\_\_\_\_1980, Working Group for Planetary System Nomenclature,
*in* 17th General Assembly, Montreal, 1979, Proceedings: International
Astronomical Union Transactions, v.17B, p.293--297.

\_\_\_\_\_\_\_1983, Working Group for Planetary System Nomenclature,
*in* 18th General Assembly, Patras, 1982, Proceedings: International
Astronomical Union Transactions, v. 18B, p. 334--336.

\_\_\_\_\_\_\_1986, Working Group for Planetary System Nomenclature,
*in* 19th General Assembly, New Delhi, 1985, Proceedings: International
Astronomical Union Transactions, v. 19B, p. 347--350.