mAl

lHl

AHi

lApc

lApd

Apu

Ap

Hp

Hpu

Hpe

eAb

lHb

eHb

HNb

lAvf

Av

AHv

lHv

lHvf

eHv

INv

Ave

lAv

Hve

Nve

lAa

Aa

ANa

AHtu

Htu

lHt

eHt

Ht

Hto

HNt

HNhu

Nhu

eHh

lNh

mNh

eNh

Nhe

mNhm

eNhm

UNIT LABEL AND

IMAGE OF TYPE

AREA

UNIT NAME AND DESCRIPTION 

(coordinates of center(s) of type area(s) 

and, where available, counting localities 

(fig. 1 and table 2))

ADDITIONAL

 CHARACTERISTICS

INTERPRETATION

LOWLAND UNITS

[Materials occupying northern lowlands (mostly –5,000 to about –4,000 m in surface elevation; low kilometer-scale surface roughness)] 

Middle Amazonian lowland unit—

Hummocky to undulating; grades 

into fields of knobs. Internally 

stratified. Tens of meters thick. 

(lat 51.43° N., long 118.45° E.)

Distributed within Vastitas Borealis 

and other northern plains; makes up 

the platforms of nearby pedestal-crater 

forms and perhaps whorled, low-relief ridge systems (thumbprint terrain, 

unmapped). Superposes units Av, AHv, 

eAb, lHl, lHt, Hpe, Hve, HNt, eHt, lNh, 

and mNh; underlies unit lApd; relation 

with unit Apu unclear

Ice-rich loess. Periglacial modification 

formed thumbprint terrain

Late Hesperian lowland unit— 

Planar to undulating; lobate 

and troughed marginal areas in 

places. Hundreds of meters to 

kilometers thick. (lat 21.40° N., 

long 118.20° E.; localities 1, 6, 

10, 11)

Continuous across most of the northern 

plains. Embays units lHt, Hto, eHt, eHv, 

HNt, lNh, mNhm, and mNh; superposed 

by units AHv, Av, eAb, Apu, mAl, lAv, 

and lApd; temporal relation to units Hpe

and Hpu unclear. Contains hundreds 

of superposed pedestal-crater forms, 

thumbprint terrain, topographically subdued wrinkle ridges, and narrow grabens 

northeast of Alba Mons 

Fluvial/lacustrine/marine and colluvial sediments sourced from circum-lowland outflow 

channels and bounding highland terrains; 

likely intercalated with and underlain by lava 

and volcaniclastic rocks. Pervasively modified and obscured by periglaciation, sedimentary diapirism, and particulate mantling

IMPACT UNIT

Amazonian and Hesperian impact 

unit—Craters with rims and surrounding blankets; some include 

single to multi-lobed blanket 

forms, dense secondary crater 

chains, and (or) central peak or pit. 

Blanket thicknesses of meters to 

a few hundred meters. (lat 23.17° 

N., long 207.77° E.)

Global occurrence. Superposes 

Noachian units; other unit superposition 

relations diverse. High kilometer-scale 

surface roughness; crater floors may be 

smooth to rough

Upturned, ejected, and brecciated target 

rocks and sediments, with local areas of 

impact melt. Post-impact mass-wasting and 

fluvial-lacustrine and eolian infill of craters 

common 

POLAR UNITS

[Mostly ice, dust, and other fines at polar latitudes; north polar outcrops occur within the northern lowlands and south polar outcrops are within 

the southern highlands. Some of the units have a relatively low dielectric constant consistent with water ice and water ice and dust mixtures]

Late Amazonian polar cap unit—

Hummocky and pitted at meter 

(northern cap) to hundreds of 

meter (southern cap) scales. Very 

high albedo except on pit floors. 

Mostly <2 m (northern cap) to <10 

m (southern cap) thick. (lat 83.00° 

N., long 317.85° E. and lat –86.04° 

N., long 291.81° E.)

Thinly caps parts of Planum Boreum 

and Planum Australe. Superposes units 

Apu and Hpu. Location of unit margin 

varies and south polar surface pits 

enlarge seasonally and annually

Residual ice (H2O in northern cap and mainly 

CO2 in southern cap) with dust lags trapped 

in north polar pits. Margins and surface of 

unit actively changing due to ice accumulation and ablation

Late Amazonian polar dunes unit—

Mounds with barchan-like, linear, 

and other dune morphologies. Low 

albedo. Marked by meter-scale 

ripples. Mounds typically tens to 

hundreds of meters across and tens 

of meters high. (lat 81.21° N., long 

217.34° E.)

Surrounds Planum Boreum. Superposes 

units mAl, lHl, Hpe, and most of Apu. 

Includes spectral detections of sulfates, 

including gypsum

Wind-blown sand organized into variety of 

dune forms owing to variable wind activity 

and permafrost development

Amazonian polar undivided unit—

Plateaus hundreds of kilometers 

across at both poles. Moderate to 

high albedo. Meters-thick layers; 

some internal unconformities; 

local lower, mostly low-albedo 

deposits unevenly bedded or 

crossbedded. Exceeds 1,000 m 

thickness in places. (lat 80.97° N., 

long 0.00° E. and lat –83.15° N., 

long 64.91° E.)

Forms Planum Australe and upper part 

of Planum Boreum. Superposes units 

lHl, Hp, Hpe, Hpu, lNh, mNh, eNh, and 

most of Ap; overlain by unit lApc and, 

except for youngest part, by unit lApd. 

Tens-of-meters-thick layers in radargrams; modified by systems of spiral 

and aligned troughs

Water ice with minor amounts of dust intermixed and as lags; local lower sequences 

made up of frozen dunes with interbedded 

ice layers

Amazonian polar unit—Plainsforming deposit. Relatively low 

radar dielectric constant. As much 

as 1,000 m thick. (lat –76.62° N., 

long 287.50° E.)

Occurs in vicinity of Cavi Angusti, near 

Planum Australe. Superposes outcrops 

of units Hp and eNh; mostly post-dated 

by unit Apu. Extensively and deeply 

pitted by Cavi Angusti

Dominantly water ice and minor lithic fines; 

pits may be thermokarst forms produced in 

part by magmatism

Hesperian polar unit—Plains-forming 

deposits marked by narrow 

sinuous, anabranching ridges and 

irregular depressions. Relatively 

low radar dielectric constant. 

Hundreds of meters thick. 

(lat –77.78° N., long 332.51° E.; 

locality 48)

Surrounds Planum Australe. Superposes 

units lNh, lNv, mNh, and eNh; gradational with unit Hpe; overlain by units 

Ap and Apu. Bumpy surface at meter 

scale

Water-ice sheets as indicated by dielectric 

constant, perhaps emplaced by cryovolcanism or from atmospheric precipitation. 

Covered by thin, periglacially deformed 

mantling deposit

Hesperian polar undivided unit—

Plateau-forming deposits. 

Decameter-thick layers. Relatively 

low radar dielectric constant. 

Locally >1,000 m thick. (lat 

80.28° N., long 302.72° E.)

Forms base of main lobe of Planum 

Boreum, including Rupes Tenuis and 

mouth of Chasma Boreale. Moderately 

low radar dielectric constant. Overlain 

by units Apu, lApd, and lApc; stratigraphic relation to unit lHl uncertain. 

Lower sequences locally cut by polygonal troughs; contains local pedestal 

crater forms 

Roughly equal proportions of water ice 

and lithic fines, possibly emplaced during 

lowland flooding events or by eolian activity. 

Deeply eroded but armored by impact material; lower sequence troughed likely due to 

compaction

Hesperian polar edifice unit—

Shields and cones having summit 

and flank depressions in polar 

regions. Relatively low radar 

dielectric constant. Hundreds of 

meters thick. (lat 75.94° N., long 

206.23° E. and lat –75.96° N., long 

341.69° E.)

Forms Scandia Tholi and Sisyphi 

Tholus. Gradational with units Hp and 

lHl; overlain by units mAl, Apu, and 

lApd. Rugged texture

Cryovolcanic or sedimentary or igneous volcanic, ice-rich constructs. Highly degraded 

by mass wasting and (or) sublimation

BASIN UNITS

[Low-lying deposits (mostly –7,000 m to slightly above –3,000 m surface elevation; low kilometer-scale surface roughness) occurring in 

and around Hellas, Argyre, and Utopia Planitiae]

Early Amazonian basin unit—Plainsforming deposits on basin floor; 

hummocky and troughed textures. 

Variable daytime IR brightness. 

Thickness <100 m in most places. 

(lat 37.44° N., long 111.17° E.; 

localities 3, 5, 41)

Occurs in central Utopia Planitia and 

western Hellas Planitia. Superposes 

units lHl, lHb, and HNb; gradational 

with units Av and AHv; superposed by 

unit mAl. Marked by wrinkle ridges in 

Hellas Planitia

Lacustrine and (or) sheet-flood deposits. Perhaps modified by compaction and 

thermokarst

Late Hesperian basin unit—Plainsforming deposits on basin floor. 

Finely layered in places. Hundreds 

of meters thick. (lat –40.80° N., 

long 64.00° E.; locality 39)

Covers central Hellas Planitia. 

Superposes units eHb, HNb, and lNv; 

embayed by unit eAb. Complex, rugged 

surface marked by scarps and ridges; 

largely bounded by marginal scarp

Ice-rich eolian, lacustrine, and (or) volcanic air-fall deposits. Margins eroded and 

back-wasted

Early Hesperian basin unit—Plainsforming deposit. Several hundred 

meters thick along contact with 

unit HNb. (lat –37.95° N., long 

78.84° E.; locality 44)

Covers eastern margins of Hellas 

Planitia. Superposes units HNb, lNh, 

lNv, and mNh; gradational with unit 

HNhu; overlain by unit lHb. Marked by 

crosscutting systems of wrinkle ridges 

and local valleys

Basin fill of eolian, lacustrine, and (or) volcanic origin. Modified by fluvial dissection. 

Tectonically contracted

Hesperian and Noachian basin 

unit—Low-lying, plains-forming 

deposit. Relatively low daytime 

IR brightness in Hellas Planitia. 

Thickness at least hundreds of 

meters. (lat –33.53° N., long

59.53° E.; locality 40)

Forms Argyre and western Hellas 

Planitiae. Embays units mNh, mNhm, 

and eNhm; gradational with unit lNv; 

overlain by units eHb, lHb, and eAb. 

Marked by wrinkle ridges and sinuous 

ridges

Basin fill of eolian, lacustrine, and (or) 

volcanic origin. Tectonically contracted. 

Sinuous ridges in Argyre Planitia interpreted 

as inverted fluvial landforms or eskers 

VOLCANIC UNITS

[Lava flows and pyroclastic deposits forming volcanoes. Flow fields erupted from fissures and centralized vents; may include local 

pyroclastic deposits. Most occurrences are likely basaltic, based on rheologic properties estimated from morphologic measurements. 

Lava plains display low kilometer-scale surface roughness]

Late Amazonian volcanic unit—

Planar deposits containing lobate 

scarps that extend hundreds to 

more than 1,000 km; sinuous 

troughs, ridges, and platy textures 

common; low-relief, shield-like 

edifices rare. Meters to tens of 

meters thick. (lat 26.27° N., long 

192.67° E.; localities 9, 21)

Covers Amazonis Planitia, southern 

Elysium Planitia, Marte Vallis, periphery of Olympus Mons, and northeast of 

Ceraunius Fossae. Superposes units Aa, 

Av, AHv, AHtu, AHi, lHv, lHl, lHt, Htu, 

eHv, eHt, eHh, HNt, lNh; gradational 

with unit lAvf and youngest parts of 

units Ave and AHv. Impact craters and 

tectonic features sparse. Contains local 

roughness and albedo variations

Largely unmodified flood lavas, including lava channels and other morphologies; 

sourced from fissures and shields

Late Amazonian volcanic field 

unit—Flows each typically tens 

of kilometers long extending 

from shields and fissure vents as 

much as tens of kilometers across. 

Meters to at least tens of meters 

thick. (lat –2.13° N., long 253.85° E.)

Occurs in central parts of Tharsis rise 

and at Cerberus Fossae. Superposes 

units Aa, lHv, eHv, HNt, and most of 

AHv; gradational with unit lAv and 

youngest parts of units Ave and AHv. 

Impact craters and tectonic features 

sparse

Largely unmodified lava flows and vents; 

vents and flows not differentiated at map 

scale

Amazonian volcanic unit—Rugged, 

hummocky, and pitted fields of 

irregular, poorly defined flows 

forming plains hundreds to more 

than 1,000 km across. Tens of 

meters or more thick. (lat 34.82° 

N., long 135.11° E.; locality 4)

Covers eastern Utopia and northern 

Amazonis Planitiae. Superposes units 

lHl and HNt and adjacent parts of unit 

AHv; gradational with unit eAb; overlain 

by units lAv, mAl, and Aa northwest of 

Olympus Mons. Subdued wrinkle ridges

Lava and perhaps volcaniclastic flows from 

Elysium Mons and unknown source northwest of Olympus Mons

Amazonian and Hesperian volcanic 

unit—Stacked, gently sloping 

lobate flows meters to tens of 

meters thick and hundreds of kilometers long. Variable daytime IR 

brightness in places. Cumulative 

thicknesses reach hundreds of 

meters to several kilometers. 

(lat –22.76° N., long 242.33° E.)

Forms bulk of the Tharsis and Elysium 

rises. Locally, superposes units lHl, Hve, 

Ht, eHh, eHt, HNt, lNh, mNh, Nhu, and 

eNh; gradational or interfingering with 

units lAvf, Ave, eAb, AHtu, lHt, lHvf, lHv, 

and eHv; overlain by units Av, mAl, lAa, 

and lAv. Low crater density in central 

part of Tharsis rise, moderate density 

elsewhere

Flood lavas and large lava flows, undifferentiated, sourced from regional fissure and vent 

systems. Highly variable ages of individual 

flows, although generally younger in central 

parts of Tharsis rise

Late Hesperian volcanic unit—

Lobate flows, meters to tens of 

meters thick and tens to hundreds 

of kilometers long; forms patches 

hundreds to more than a thousand kilometers across. Variable 

daytime IR brightness in places. 

Hundreds of meters or more total 

thickness. (lat –18.84° N., long 

256.12° E.; localities 17, 29)

Distributed occurrence in Tharsis 

region, southwestern Hesperia Planum, 

and Orcus Patera. Superposes units 

eHv, eHh, lNh, Nhu, Nhe, Nve, mNh, 

eNh, and eNhm; gradational with units 

lHvf and Hve; overlain by units AHv, 

AHtu, ANa (Amazonian part), Aa, lAv, 

and lAvf. Largest patch in Syria Planum 

region deeply dissected by troughs 

and grabens of Noctis Labyrinthus and 

Noctis Fossae

Flood lavas and large lava flows, undifferentiated, sourced from regional fissure and vent 

systems

Late Hesperian volcanic field unit—

Patches hundreds of kilometers 

across of lobate flows typically 

meters thick and tens of kilometers 

long emanating from low shields 

and fissure vents kilometers to tens 

of kilometers across. Hundreds 

of meters or more total thickness. 

(lat –12.31° N., long 257.63° E.)

Distributed occurrence in Syria Planum, 

western Tempe Terra, southwest of 

Ceraunius Fossae, western Elysium 

Mons, and Orcus Patera. Superposes 

units eHh, HNt, lNh, mNh; gradational 

or interfingers with units lHv, Hve, and 

AHv; overlain by unit ANa (Amazonian 

part). Locally modified by troughs and 

fissures

Volcanoes and lava flows 

Early Hesperian volcanic unit—

Planar deposits meters to tens of 

meters thick and tens to hundreds 

of kilometers across; lobate scarps 

common. Variable daytime IR 

brightness in places. Hundreds of 

meters or more total thickness. 

(lat –25.34° N., long 279.97° E.; 

localities 38, 42)

High plains within and near Tharsis 

rise, Syrtis Major and Hesperia Plana, 

and Gusev crater. Superposes units 

HNt, HNhu, lNv, lNh, Nhu, Nhe, Nve, 

mNh, mNhm, eNh, and eNhm; gradational with units eHt, eHh, Ht, and Hve; 

overlain by units Hto, lHv, lHt, lHl, AHv, 

AHtu, lAv, and lAvf. Marked by wrinkle 

ridges

Flood lavas, undifferentiated, sourced 

from regional fissure and vent systems. 

Tectonically contracted

Late Noachian volcanic unit—Planar 

deposits meters to tens of meters 

thick and tens to hundreds of kilometers across; lobate scarps sparse 

and indistinct. Variable daytime 

IR brightness in places. Hundreds 

of meters or more total thickness. 

(lat –55.89° N., long 67.99° E.; 

localities 46, 47)

Occurs in Malea and Thaumasia Plana, 

Icaria Fossae area, and east of Hellas 

Planitia. Superposes units Nhe, mNh, 

eNh, and eNhm; gradational with units 

lNh, HNb, Nhu, and Nve; overlain by 

units eHv, eHh, eHb, lHb, Hp, HNt

(Hesperian part), AHv, and Aa. Includes 

some degraded craters; marked by wrinkle ridges

Degraded lava and volcaniclastic flows. 

Tectonically contracted

Amazonian volcanic edifice—Shieldlike edifices hundreds of kilometers across; made up of lobate 

flows meters to tens of meters 

thick and tens to hundreds of 

kilometers across. Edifices several 

to more than ten kilometers high. 

(lat 18.89° N., long 225.86° E.)

Forms Olympus, Alba, Ascraeus, 

Pavonis, and Arsia Montes. Younger 

part superposes units Aa and AHtu; 

gradational with units lAvf, and AHv; 

overlain by unit lAa. Deformed by 

summit calderas tens to >100 km wide 

and circumferential scarp systems

Volcanic edifices composed of lava flows 

and possible volcaniclastic rocks. Deformed 

by summit collapse from magma withdrawal 

and gravity spreading of flanks

Hesperian volcanic edifice unit—

Shield-like edifices several tens 

to hundreds of kilometers across; 

made up of lobate flows meters 

to tens of meters thick and tens 

to hundreds of kilometers across, 

as well as dissected layers tens 

of meters thick. As much as few 

kilometers thick. (lat 24.65° N., 

long 146.80° E.)

Occurs at Tharsis and Elysium rises, 

Hadriacus Mons, and Apollinaris Mons 

south flank. Superposes unit eNhm; 

gradational with units lHv, lHvf, lHt, lHl, 

eHv, and HNt (Hesperian part); overlain by unit AHv. Some outcrops have 

summit calderas tens of kilometers 

across; some radiating valleys 

Volcanic edifices composed of different combinations of lava flows and pyroclastic and 

volcaniclastic deposits. Modified by summit 

collapse from magma withdrawal and fluvial 

dissection in places

Noachian volcanic edifice unit—

Shield-like edifices several tens 

to hundreds of kilometers across; 

lobate flow morphologies indistinct or absent. As much as few 

kilometers thick. (lat –8.11° N., 

long 174.50° E.)

Occurrences include Amphitrites and 

Peneus Paterae, Tyrrhenus Mons, 

northern Apollinaris Mons, and southern 

Tharsis rise. Gradational with units lNv, 

mNh, eNh, and HNt (Noachian part); 

overlain by units HNt (Hesperian part), 

eHv, lHv, Hve, Htu, AHtu, and AHv. 

Heavily cratered; some outcrops have 

summit depressions tens of kilometers 

across; marked by irregular scarps and 

ridges; some radiating valleys

Volcanic edifices composed of different combinations of lava flows, pyroclastic deposits, 

and volcaniclastic deposits sourced from 

degraded shields. Domed and fractured by 

local intrusions. Tectonically contracted

APRON UNITS

Late Amazonian apron unit—

Concentrically ribbed, knobby 

lobes extending as much as 500 

km from shield-like edifices. 

Meters (or less) to tens-of-meters 

thick. (lat 4.33° N., long 243.07° 

E.)

Covers northwest peripheries of Tharsis 

and Olympus Montes. Superposes 

units Aa, Ave, and AHv. Craters sparse; 

underlying lobate flows only moderately 

subdued by distal parts of unit

Drop moraines left by cold-based glaciers 

Amazonian apron unit—Lobes 

bounded by scarps tens to hundreds of kilometers across, marked 

by transverse ridges few kilometers wide and tens of kilometers 

long; linear grooves in places. As 

much as 1,000 m thick. (lat –8.04° 

N., long 281.80° E. and lat 30.17° 

N., long 214.65° E.)

Surrounds Olympus Mons and covers 

parts of walls and floors of Valles 

Marineris. Superposes units Av, lHt, lHv, 

eHh, Ht, Htu, lNh, lNv, and Nhu; overlain 

by units lAv, lAa, lAvf, AHtu, and youngest part of Ave

Landslide and gravity-spreading deposits 

derived from flanks of Olympus Mons and 

walls of Valles Marineris

Amazonian and Noachian apron 

unit—Irregular knobs and mesas 

tens of kilometers across and 

aprons extending tens of kilometers from them. Aprons hundreds 

of meters thick. (lat –43.22° N., 

long 26.66° E.)

Occurs in Deuteronilus and Protonilus 

Mensae and east of Hellas Planitia. 

Noachian part gradational with units 

HNt, lNh, mNh, and eNhm and overlain 

by unit AHi. Amazonian part embays 

units AHv, lHv, lHvf, lHt, eHv, eHt, 

HNhu, lNh, mNh, and eNhm; gradational 

with HNt (Hesperian part). Aprons 

sparsely cratered, locally grooved and 

pitted, and in places display low-radar-dielectric constant

Ice-rich Amazonian materials derived from 

air-fall and mass-wasting erosion and transported by mass flow and underlying, relict 

Noachian highland materials. Modified by 

thermokarst processes

TRANSITION UNITS

[Materials occupying highland/lowland marginal zones and dissected areas of highland terrain (mostly just above –4,000 to –1,000 m 

surface elevation). Mass-wasting, sedimentary, and possibly volcanic origins likely. Units may include knobs and mesas of highland 

materials too small to map separately]

Amazonian and Hesperian transition undivided unit—Irregularly 

shaped plateaus hundreds to more 

than one thousand kilometers 

across. Locally layered. Hundreds 

of meters to ~3,000 m thick. 

(lat –2.37° N., long 240.33° E.; 

localities 25, 27, 30)

Occurs along highland/lowland boundary from Olympus Mons to southwestern Elysium Planitia and as one 

small outcrop west of Kasei Valles. 

Superposes units Aa, Ave, lHv, lHt, eHv, 

eHt, Htu, HNt, Nve, mNh, and eNh; 

interfingers with unit AHv; overlain 

by unit lAv. Marked by dense linear 

ridges, grooves, and scarps hundreds of 

meters wide and tens of kilometers long; 

includes subdued and pedestal-crater 

forms

Fine-grained eolian sediments and (or) pyroclastic air-fall deposits. Linear ridges and 

grooves form yardangs

Hesperian transition undivided 

unit—Irregular plateaus hundreds 

of kilometers across. Layered. 

Hundreds of meters to kilometers 

thick. (lat –6.41° N., long 156.42° 

E; lat –6.17° N., long 286.05° E.; 

localities 26, 28)

In southern Elysium Planitia along 

highland/lowland boundary and within 

and east of Valles Marineris. Superposes 

units Nhu, Nve, mNh, and eNh; gradational with units eHt, Hve, and HNt

(Hesperian part); overlain by units lHt, 

Ht, Hto, AHtu, Aa, and lAv. Includes 

hydrated sulfate spectral signatures; 

fluted slopes in places. Linear ridges, 

anabranching sinuous ridges, and wrinkle ridges common

Fine-grained eolian sediments and (or) pyroclastic air-fall deposits. Modified by fluvial 

dissection and eolian erosion. Linear ridges 

and grooves form yardangs. Tectonically 

contracted. Channels mostly inverted. 

Altered by acidic weathering in places

Late Hesperian transition unit—

Plains-forming deposits, relatively 

smooth; includes small knobs and 

mesas of Noachian and perhaps 

younger material. May be tens 

to hundreds of meters thick. (lat 

18.13° N., long 117.11° E.; localities 8, 15)

Occurs along highland/lowland boundary, near Phlegra Montes, on and alongside Valles Marineris and on several 

crater floors, and at Acidalia Mensa 

and southeast of Hesperia Planum. 

Superposes units eHt, eHv, eHh, Htu, 

HNt, Nhu, mNh, mNhm, and eNh; 

gradational with unit Hve; interfingers 

with unit AHv, overlain by units Hto, lHl, 

AHtu, Aa, mAl, lAv, and younger part 

of ANa. Moderate density of wrinkle 

ridges; dense branching valleys near 

Echus Chasma

Mass-wasting, fluvial/lacustrine, and possibly other sedimentary materials and volcanic 

rocks in places. Tectonically contracted 

Early Hesperian transition unit—

Plains-forming deposits, undulating to moderately rugged; includes 

scattered low knobs and mesas 

of Noachian highland material. 

May be tens to hundreds of meters 

thick. (lat 13.38° N., long 116.70° 

E.; localities 2, 16)

Abutting the highland/lowland boundary, Arcadia and southwestern Amazonis 

Planitiae, and Acidalia Mensa. 

Superposes units lNh, Nhu, mNh, mNhm, 

and eNh; gradational with units Htu, HNt

(Hesperian part), and eHv; overlain by 

units Ht, Hto, lHl, lHt, AHv, AHtu, mAl, 

lAv, and younger part of ANa. Moderate 

density of wrinkle ridges

Mass-wasting, fluvial/lacustrine, and other 

sedimentary materials and possibly volcanic 

rocks in places. Tectonically contracted 

Hesperian transition unit—Knobs, 

mesas, and intervening aprons and 

plains within highland canyons 

and chaotic terrain. Hundreds of 

meters thick. (lat 1.75° N., long 

325.45° E.)

Occurs in topographic lows in Xanthe 

and Margaritifer Terrae and north of 

Valles Marineris. Superposes units eHt, 

eHh, eHv, lNh, mNh, Nhu, and eNh; gradational with unit Hto; overlain by units 

Htu, lHt, AHv, and Aa

Mixture of sediments and blocks of broken 

up, mass-wasted, and collapsed materials

Hesperian transition outflow unit—

Plains deposits in places dissected 

by tens-of-kilometers-wide 

anabranching channel systems. 

Relatively bright in nighttime IR 

in Maja Valles. Meters to at least 

tens of meters thick. (lat 19.33° N., 

long 326.45° E.—Mars Pathfinder 

landing site; locality 12)

Covers Chryse Planitia, eastern Lunae 

Planum, and canyons in Xanthe and 

Margaritifer Terrae. Superposes units 

AHv, lHt, eHh, eHv, eHt, lNh, mNh, Nhu, 

and eNh; gradational with unit Ht; overlain by unit lHl

Outflow channel fluvial and debris-flow 

deposits from catastrophic erosion of highland rocks; islands of underlying bedrock 

exposed

Hesperian and Noachian transition 

unit—Knobs, mesas, and intervening aprons and plains. May be 

tens to hundreds of meters thick. 

(lat 10.96° N., long 111.71° E.; 

locality 18)

Occurs adjacent to Noachian highland materials along highland/lowland 

boundary except in lowlands east of 

Elysium rise and near Acidalia Mensa. 

Noachian part gradational with units 

eNh, mNh, mNhm, lNh, Nve, and 

Noachian part of ANa. Hesperian part 

superposes units lNv, Nve, Nhe, Nhu, 

mNh, mNhm, and eNh; gradational 

with units eHt, eHh, Htu, Hve, and 

Amazonian part of ANa; overlain by 

units eHv, lHt, lHl, lHvf, AHtu, AHv, AHi, 

Av, mAl, lAv, and lAvf. Marked by predominantly north-south-oriented wrinkle 

ridges

Noachian impact breccias, sediments, and 

volcanic deposits with intervening aprons 

of Hesperian mass-wasted materials. 

Tectonically contracted

HIGHLAND UNITS

[Materials forming densely cratered midland and highland areas (generally ~3,000 m to 5,000 m in surface elevation, down to less than 

–6,000 m in Hellas Planitia; high kilometer-scale surface roughness). Dominated by complex admixtures of impact, sedimentary, and 

volcanic rocks]

Hesperian and Noachian highland 

undivided unit—Mound forming. Light toned in visible images. 

Layered. Hundreds of meters to 

several kilometers thick. (lat 5.97° 

N., long 2.33° E.; locality 24)

Occurs on Meridiani Planum, in some 

highland craters, and east of Hellas 

Planitia. Superposes units eHh, lNh 

(except gradational east of Hellas 

Planitia), mNh, eNh, and eNhm; 

gradational with unit eHb; overlain by 

units eHv and ANa (Amazonian part). 

Includes hydrated sulfate spectral 

signatures

Undifferentiated, friable (likely fine grained) 

sedimentary, volcanic, and impact rocks. 

Altered by weathering

Noachian highland undivided unit—

Forms canyon walls and some 

high plains and channel floors. 

Layered. Hundreds of meters to 

several kilometers thick in exposures. (lat –25.80° N., long 288.53° 

E.; locality 37)

Occurs in Valles Marineris walls; in 

eastern Thaumasia and Malea Plana; and 

along Kasei, Ares, and Mangala Valles. 

Gradational with units lNh, lNv, mNh, 

and eNh; overlain by units eHh, eHv, 

eHt, Hp, Htu, Ht, Hto, HNt (Hesperian 

part), lHv, lHt, AHv, and Aa. Marked in 

places by wrinkle ridges and valleys

Undifferentiated friable sedimentary, impact, 

and volcanic materials. Tectonically contracted in places

Early Hesperian highland unit—

High plains-forming, relatively 

smooth outcrops extending hundreds of kilometers. May be hundreds of meters thick. (lat 15.88° 

N., long 293.44° E.)

Occurs on plateaus surrounding Tharsis 

rise and in scattered highland lows. 

Superposes units lNh, lNv, Nhu, mNh, 

mNhm, eNh, and eNhm; gradational 

with units eHv and HNt (Hesperian part); 

overlain by units HNhu (in Schiaparelli 

crater), Hto, lHv, lHvf, lHt, AHv, Aa, 

and lAv. Knobby, wrinkle-ridged, and 

dissected in places

Undifferentiated impact, volcanic, eolian, 

fluvial/lacustrine materials. Locally degraded 

and (or) deformed

Late Noachian highland unit—

Mostly plains forming, rugged in 

places. May be hundreds of meters 

thick. (lat –20.74° N., long 354.35° 

E.; localities 13, 34, 35)

Occurs commonly in highland depressions, as well as sparsely in higher-elevation parts of the lowlands. Superposes 

units mNh, mNhm, eNh, and eNhm; 

gradational with units lNv, Nhu and HNt

and ANa (Noachian parts); overlain by 

units HNhu, eHv, eHh, eHt, eHb, Hp, 

Ht, Hto, lHl, lHv, lHvf, AHv, Apu, Aa, 

and lAv. Locally marked by grabens or 

wrinkle ridges

Undifferentiated impact, volcanic, fluvial, and basin material. Lightly to heavily 

degraded and (or) deformed

Middle Noachian highland unit—

Uneven to rolling topography; 

high-relief outcrops that extend 

hundreds to thousands of kilometers. Commonly layered in crater 

walls. May be hundreds of meters 

to more than a kilometer thick. 

(lat –47.17° N., long 349.33° E.; 

localities 7, 14, 19, 20, 22, 23, 31)

Extensive in the equatorial to southern 

highlands. Superposes units eNh and 

eNhm; gradational with units mNhm, 

Nhu, Nhe, Nve, and HNt and ANa

(Noachian parts); overlain by units lNh, 

lNv, HNt (Hesperian part), HNhu, HNb, 

eHb, eHv, eHh, eHt, Hp, Ht, Hto, Htu, 

lHl, lHv, lHvf, ANa, AHtu, AHv, Apu, mAl, 

and lAv. Heavily cratered and marked 

by locally dense valleys, grabens, and 

wrinkle ridges

Undifferentiated impact, volcanic, fluvial, 

and basin materials. Moderately to heavily 

degraded

Early Noachian highland unit—

Rugged, very high relief outcrops 

extending hundreds of kilometers. 

Thickness commonly exceeds a 

few kilometers but ill-defined. 

(lat –20.74° N., long 354.35° E; 

localities 33, 36)

Covers large parts of equatorial and 

southern highlands but sparse surrounding Argyre basin, in Arabia Terra, 

and near highland/lowland boundary. 

Gradational with units HNt (Noachian 

part), Nhu, Nhe, Nve, mNhm, and eNhm; 

overlain by mNh, lNh, lNv, HNhu, HNt

(Hesperian part), eHv, lHv, lHt, Hp, Hto, 

AHv, AHtu, AHi, Apu. Densely cratered; 

marked by broad, linear and irregular 

scarps and ridges

Undifferentiated impact, volcanic, fluvial, 

and basin materials. Heavily degraded; tectonically deformed in places

Noachian highland edifice unit—

Irregular edifices marked by 

troughs and peaks. As much as a 

few kilometers thick. (lat –34.72° 

N., long 214.85° E.)

Occurs in southern highlands mostly lat 

30° to 70° S., especially south of Tharsis 

region. Gradational with units HNt, lNh, 

mNh and eNh; overlain by units lNh, 

lNv, HNt (Hesperian part), eHv, lHv, and 

AHv. Densely cratered and marked by 

scarps and ridges

Mainly undifferentiated, degraded volcanic 

materials. Heavily degraded and tectonically 

modified 

Middle Noachian highland massif 

unit—High-relief massifs tens 

of kilometers across separated by 

broad linear troughs and valleys. 

Kilometers thick. (lat –44.48° N., 

long 307.54° E.)

Surrounds Argyre and part of Isidis 

Planitiae. Gradational with units mNh, 

eNh, and HNt (Noachian part); overlain 

by units lNh, HNb, HNt (Hesperian part), 

eHh, eHt, eHv, lHt, and lHl. Heavily cratered; dissected by grabens and valleys 

in places

Ancient, degraded crustal rocks uplifted by 

large, basin-forming impacts. Dissected by 

basin-related fault structures and erosional 

valleys

Early Noachian highland massif 

unit—Forms high-relief massifs 

tens of kilometers across separated 

by broad linear troughs and valleys. Kilometers thick. (lat –26.00° 

N., long 63.24° E.; localities 43, 

45)

Forms annulus around most of Hellas 

Planitia. Gradational with units eNh and 

ANa (Noachian part); overlain by units 

mNh, lNh, lNv, HNb, HNhu, eHv, Hve, 

and lHv. Heavily cratered; dissected by 

valleys in places

Primitive, degraded crustal rocks uplifted by 

large, basin-forming impact. Dissected by 

basin-related fault structures and erosional 

valleys

VOLCANIC UNITS—Continued

[Lava flows and pyroclastic deposits forming volcanoes. Flow fields erupted from fissures and centralized vents; may include local 

pyroclastic deposits. Most occurrences are likely basaltic, based on rheologic properties estimated from morphologic measurements. 

Lava plains display low kilometer-scale surface roughness]

UNIT LABEL AND

IMAGE OF TYPE

AREA

UNIT NAME AND DESCRIPTION 

(coordinates of center(s) of type area(s) 

and, where available, counting localities 

(fig. 1 and table 2))

ADDITIONAL

 CHARACTERISTICS

DESCRIPTION OF MAP UNITS INTERPRETATION

[Note: Unit groups and labels are discussed in pamphlet. Unit definitions include morphologic character, infrared brightness or albedo (where diagnostic), nature 

of stratification (if observed), and typical unit thickness (where top and bottom of unit identified and assuming flat-lying materials; measured or estimated using 

MOLA elevation data). Additional characteristics include location, complete record of observed superposition relations with other map units (except with unit AHi, 

which displays complex age relations with other units), and other secondary and (or) local characteristics and associations including morphologies, spectrally 

based compositional information, and radar-sounding properties. See Geologic Summary in pamphlet for further discussion of map units, including references; 

tables 2 (locality numbers) and 3 and fig. 1 for crater-density data; and tables 6 and 7 for comparison with Viking-based, global mapping units]

Tanaka, K.L., Skinner, J.A., Jr., Dohm J.M., Irwin, R.P., III, Kolb, E.J., 

Fortezzo, C.M., Platz, T., Michael, G.G., and Hare, T.M., 2014, 

Geologic map of Mars: U.S. Geological Survey Scientific 

Investigations Map 3292, scale 1:20,000,000, pamphlet 43 p., 

http://dx.doi.org/10.3133/sim3292.