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Home , Alba Mons, Amazonian (Mars), Cerberus (Mars), Hesperian, Hesperia Planum, Mensa (geology)

DESCRIPTION OF MAP UNITS UNIT LABEL AND UNIT NAME AND DESCRIPTION ADDITIONAL INTERPRETATION [Note: Unit groups and labels are discussed in pamphlet. Unit definitions include morphologic character, infrared brightness or albedo (where diagnostic), nature IMAGE OF TYPE (coordinates of center(s) of type area(s) CHARACTERISTICS of stratification (if observed), and typical unit thickness (where top and bottom of unit identified and assuming flat-lying materials; measured or estimated using AREA and, where available, counting localities MOLA elevation data). Additional characteristics include location, complete record of observed superposition relations with other map units (except with unit AHi, (fig. 1 and table 2)) which displays complex relations with other units), and other secondary and (or) local characteristics and associations including morphologies, spectrally VOLCANIC UNITS—Continued based compositional information, and radar-sounding properties. See Geologic Summary in pamphlet for further discussion of map units, including references; [ flows and pyroclastic deposits forming volcanoes. Flow fields erupted from fissures and centralized vents; may include local 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] 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 UNIT NAME AND DESCRIPTION ADDITIONAL INTERPRETATION Hve volcanic edifice unit— Occurs at and Elysium rises, Volcanic edifices composed of different com- IMAGE OF TYPE (coordinates of center(s) of type area(s) CHARACTERISTICS Shield-like edifices several tens , and binations of lava flows and pyroclastic and AREA and, where available, counting localities to hundreds of kilometers across; flank. Superposes unit eNhm; volcaniclastic deposits. Modified by summit (fig. 1 and table 2)) made up of lobate flows meters gradational with units lHv, lHvf, lHt, lHl, collapse from magma withdrawal and fluvial LOWLAND UNITS to tens of meters thick and tens eHv, and HNt (Hesperian part); over- dissection in places [Materials occupying northern lowlands (mostly –5,000 to about –4,000 m in surface elevation; low kilometer-scale surface roughness)] to hundreds of kilometers across, lain by unit AHv. Some have as well as dissected layers tens summit tens of kilometers mAl Middle lowland unit— Distributed within Ice-rich loess. Periglacial modification of meters thick. As much as few across; some radiating valleys Hummocky to undulating; grades and other northern plains; makes up formed thumbprint kilometers thick. (lat 24.65° N., into fields of knobs. Internally the platforms of nearby pedestal-crater long 146.80° E.) stratified. Tens of meters thick. forms and perhaps whorled, low-re- (lat 51.43° N., long 118.45° E.) lief ridge systems (thumbprint terrain, Nve volcanic edifice unit— Occurrences include Amphitrites and Volcanic edifices composed of different com- unmapped). Superposes units Av, AHv, Shield-like edifices several tens Peneus Paterae, , binations of lava flows, pyroclastic deposits, eAb, lHl, lHt, Hpe, Hve, HNt, eHt, lNh, to hundreds of kilometers across; northern Apollinaris Mons, and southern and volcaniclastic deposits sourced from and mNh; underlies unit lApd; relation lobate flow morphologies indis- Tharsis rise. Gradational with units lNv, degraded shields. Domed and fractured by with unit Apu unclear tinct or absent. As much as few mNh, eNh, and HNt (Noachian part); local intrusions. Tectonically contracted kilometers thick. (lat –8.11° N., overlain by units HNt (Hesperian part), lHl Late Hesperian lowland unit— Continuous across most of the northern Fluvial/lacustrine/marine and colluvial sedi- long 174.50° E.) eHv, lHv, Hve, Htu, AHtu, and AHv. Planar to undulating; lobate plains. Embays units lHt, Hto, eHt, eHv, ments sourced from circum-lowland outflow Heavily cratered; some outcrops have and troughed marginal areas in HNt, lNh, mNhm, and mNh; superposed channels and bounding highland ; summit depressions tens of kilometers places. Hundreds of meters to by units AHv, Av, eAb, Apu, mAl, lAv, likely intercalated with and underlain by lava across; marked by irregular scarps and kilometers thick. (lat 21.40° N., and lApd; temporal relation to units Hpe and volcaniclastic rocks. Pervasively modi- ridges; some radiating valleys long 118.20° E.; localities 1, 6, and Hpu unclear. Contains hundreds fied and obscured by periglaciation, sedi- APRON UNITS 10, 11) of superposed pedestal-crater forms, mentary diapirism, and particulate mantling thumbprint terrain, topographically sub- lAa Late Amazonian apron unit— Covers northwest peripheries of Tharsis Drop moraines left by cold-based dued wrinkle ridges, and narrow Concentrically ribbed, knobby and Olympus Montes. Superposes northeast of lobes extending as much as 500 units Aa, Ave, and AHv. Craters sparse; IMPACT UNIT km from shield-like edifices. underlying lobate flows only moderately Meters (or less) to tens-of-meters subdued by distal parts of unit AHi Amazonian and Hesperian impact Global occurrence. Superposes Upturned, ejected, and brecciated target thick. (lat 4.33° N., long 243.07° unit—Craters with rims and sur- Noachian units; other unit superposition rocks and sediments, with local areas of E.) rounding blankets; some include relations diverse. High kilometer-scale impact melt. Post-impact mass-wasting and single to multi-lobed blanket surface roughness; crater floors may be fluvial-lacustrine and eolian infill of craters Aa Amazonian apron unit—Lobes Surrounds and covers Landslide and gravity-spreading deposits forms, dense secondary crater smooth to rough common bounded by scarps tens to hun- parts of walls and floors of Valles derived from flanks of Olympus Mons and Av lHt lHv chains, and (or) central peak or pit. dreds of kilometers across, marked Marineris. Superposes units , , , walls of eHh Ht Htu lNh lNv Nhu Blanket thicknesses of meters to by transverse ridges few kilome- , , , , , and ; overlain lAv lAa lAvf AHtu a few hundred meters. (lat 23.17° ters wide and tens of kilometers by units , , , , and young- Ave N., long 207.77° E.) long; linear grooves in places. As est part of much as 1,000 m thick. (lat –8.04° POLAR UNITS N., long 281.80° E. and lat 30.17° [Mostly ice, , and other fines at polar ; north polar outcrops occur within the northern lowlands and south polar outcrops are within N., long 214.65° E.) the southern highlands. Some of the units have a relatively low dielectric constant consistent with water ice and water ice and dust mixtures]

lApc Late Amazonian polar cap unit— Thinly caps parts of Residual ice (H2O in northern cap and mainly ANa Amazonian and Noachian apron Occurs in Deuteronilus and Protonilus Ice-rich Amazonian materials derived from Hummocky and pitted at meter and . Superposes units CO2 in southern cap) with dust lags trapped unit—Irregular knobs and mesas Mensae and east of . air-fall and mass-wasting erosion and trans- (northern cap) to hundreds of Apu and Hpu. Location of unit margin in north polar pits. Margins and surface of tens of kilometers across and Noachian part gradational with units ported by mass flow and underlying, relict meter (southern cap) scales. varies and south polar surface pits unit actively changing due to ice accumula- aprons extending tens of kilome- HNt, lNh, mNh, and eNhm and overlain Noachian highland materials. Modified by high albedo except on pit floors. enlarge seasonally and annually tion and ablation ters from them. Aprons hundreds by unit AHi. Amazonian part embays thermokarst processes Mostly <2 m (northern cap) to <10 of meters thick. (lat –43.22° N., units AHv, lHv, lHvf, lHt, eHv, eHt, m (southern cap) thick. (lat 83.00° long 26.66° E.) HNhu, lNh, mNh, and eNhm; gradational N., long 317.85° E. and lat –86.04° with HNt (Hesperian part). Aprons N., long 291.81° E.) sparsely cratered, locally grooved and pitted, and in places display low-ra- lApd Late Amazonian polar dunes unit— Surrounds Planum Boreum. Superposes -blown sand organized into variety of dar-dielectric constant Mounds with barchan-like, linear, units mAl, lHl, Hpe, and most of Apu. dune forms owing to variable wind activity TRANSITION UNITS and other dune morphologies. Low Includes spectral detections of sulfates, and permafrost development [Materials occupying highland/lowland marginal zones and dissected areas of highland terrain (mostly just above –4,000 to –1,000 m albedo. Marked by meter-scale including gypsum surface elevation). Mass-wasting, sedimentary, and possibly volcanic origins likely. Units may include knobs and mesas of highland ripples. Mounds typically tens to materials too small to map separately] hundreds of meters across and tens of meters high. (lat 81.21° N., long AHtu Amazonian and Hesperian transi- Occurs along highland/lowland bound- Fine-grained eolian sediments and (or) pyro- 217.34° E.) tion undivided unit—Irregularly ary from Olympus Mons to south- clastic air-fall deposits. Linear ridges and shaped plateaus hundreds to more western and as one grooves form yardangs Apu Amazonian polar undivided unit— Forms Planum Australe and upper part Water ice with minor amounts of dust inter- than one thousand kilometers small west of . Plateaus hundreds of kilometers of Planum Boreum. Superposes units mixed and as lags; local lower sequences across. Locally layered. Hundreds Superposes units Aa, Ave, lHv, lHt, eHv, across at both poles. Moderate to lHl, Hp, Hpe, Hpu, lNh, mNh, eNh, and made up of frozen dunes with interbedded of meters to ~3,000 m thick. eHt, Htu, HNt, Nve, mNh, and eNh; high albedo. Meters-thick layers; most of Ap; overlain by unit lApc and, ice layers (lat –2.37° N., long 240.33° E.; interfingers with unit AHv; overlain some internal ; except for youngest part, by unit lApd. localities 25, 27, 30) by unit lAv. Marked by dense linear local lower, mostly low-albedo Tens-of-meters-thick layers in radar- ridges, grooves, and scarps hundreds of deposits unevenly bedded or grams; modified by systems of spiral meters wide and tens of kilometers long; crossbedded. Exceeds 1,000 m and aligned troughs includes subdued and pedestal-crater thickness in places. (lat 80.97° N., forms long 0.00° E. and lat –83.15° N., long 64.91° E.) Htu Hesperian transition undivided In southern Elysium Planitia along Fine-grained eolian sediments and (or) pyro- unit—Irregular plateaus hundreds highland/lowland boundary and within clastic air-fall deposits. Modified by fluvial Ap Amazonian polar unit—Plains- Occurs in vicinity of Cavi Angusti, near Dominantly water ice and minor lithic fines; of kilometers across. Layered. and east of Valles Marineris. Superposes dissection and eolian erosion. Linear ridges forming deposit. Relatively low Planum Australe. Superposes outcrops pits may be thermokarst forms produced in Hundreds of meters to kilometers units Nhu, Nve, mNh, and eNh; gra- and grooves form yardangs. Tectonically radar dielectric constant. As much of units Hp and eNh; mostly post-dated part by magmatism thick. (lat –6.41° N., long 156.42° dational with units eHt, Hve, and HNt contracted. Channels mostly inverted. as 1,000 m thick. (lat –76.62° N., by unit Apu. Extensively and deeply E; lat –6.17° N., long 286.05° E.; (Hesperian part); overlain by units lHt, Altered by acidic in places long 287.50° E.) pitted by Cavi Angusti localities 26, 28) Ht, Hto, AHtu, Aa, and lAv. Includes hydrated sulfate spectral signatures; Hp Hesperian polar unit—Plains-forming Surrounds Planum Australe. Superposes Water-ice sheets as indicated by dielectric fluted slopes in places. Linear ridges, deposits marked by narrow units lNh, lNv, mNh, and eNh; grada- constant, perhaps emplaced by cryovolca- anabranching sinuous ridges, and wrin- sinuous, anabranching ridges and tional with unit Hpe; overlain by units nism or from atmospheric precipitation. kle ridges common irregular depressions. Relatively Ap and Apu. Bumpy surface at meter Covered by thin, periglacially deformed low radar dielectric constant. scale mantling deposit lHt Late Hesperian transition unit— Occurs along highland/lowland bound- Mass-wasting, fluvial/lacustrine, and possi- Hundreds of meters thick. Plains-forming deposits, relatively ary, near , on and along- bly other sedimentary materials and volcanic (lat –77.78° N., long 332.51° E.; smooth; includes small knobs and side Valles Marineris and on several rocks in places. Tectonically contracted locality 48) mesas of Noachian and perhaps crater floors, and at Acidalia younger material. May be tens and southeast of . Hpu Hesperian polar undivided unit— Forms base of lobe of Planum Roughly equal proportions of water ice to hundreds of meters thick. (lat Superposes units eHt, eHv, eHh, Htu, Plateau-forming deposits. Boreum, including Rupes Tenuis and and lithic fines, possibly emplaced during 18.13° N., long 117.11° E.; locali- HNt, Nhu, mNh, mNhm, and eNh; Decameter-thick layers. Relatively mouth of Boreale. Moderately lowland flooding events or by eolian activity. ties 8, 15) gradational with unit Hve; interfingers low radar dielectric constant. low radar dielectric constant. Overlain Deeply eroded but armored by impact mate- with unit AHv, overlain by units Hto, lHl, Locally >1,000 m thick. (lat by units Apu, lApd, and lApc; strati- rial; lower sequence troughed likely due to AHtu, Aa, mAl, lAv, and younger part 80.28° N., long 302.72° E.) graphic relation to unit lHl uncertain. compaction of ANa. Moderate density of wrinkle Lower sequences locally cut by polyg- ridges; dense branching valleys near onal troughs; contains local pedestal crater forms eHt Early Hesperian transition unit— Abutting the highland/lowland bound- Mass-wasting, fluvial/lacustrine, and other Hpe Hesperian polar edifice unit— Forms Scandia Tholi and Sisyphi Cryovolcanic or sedimentary or igneous vol- Plains-forming deposits, undulat- ary, Arcadia and southwestern Amazonis sedimentary materials and possibly volcanic Shields and cones having summit . Gradational with units Hp and canic, ice-rich constructs. Highly degraded ing to moderately rugged; includes Planitiae, and Acidalia Mensa. rocks in places. Tectonically contracted and flank depressions in polar lHl; overlain by units mAl, Apu, and by and (or) sublimation scattered low knobs and mesas Superposes units lNh, Nhu, mNh, mNhm, regions. Relatively low radar lApd. Rugged texture of Noachian highland material. and eNh; gradational with units Htu, HNt dielectric constant. Hundreds of May be tens to hundreds of meters (Hesperian part), and eHv; overlain by meters thick. (lat 75.94° N., long thick. (lat 13.38° N., long 116.70° units Ht, Hto, lHl, lHt, AHv, AHtu, mAl, 206.23° E. and lat –75.96° N., long E.; localities 2, 16) lAv, and younger part of ANa. Moderate 341.69° E.) density of wrinkle ridges

Ht Hesperian transition unit—Knobs, Occurs in topographic lows in Xanthe Mixture of sediments and blocks of broken mesas, and intervening aprons and and Margaritifer Terrae and north of up, mass-wasted, and collapsed materials BASIN UNITS plains within highland canyons Valles Marineris. Superposes units eHt, [Low-lying deposits (mostly –7,000 m to slightly above –3,000 m surface elevation; low kilometer-scale surface roughness) occurring in and chaotic terrain. Hundreds of eHh, eHv, lNh, mNh, Nhu, and eNh; gra- and around Hellas, Argyre, and Utopia Planitiae] meters thick. (lat 1.75° N., long dational with unit Hto; overlain by units eAb Early Amazonian basin unit—Plains- Occurs in central and Lacustrine and (or) sheet-flood depos- 325.45° E.) Htu, lHt, AHv, and Aa forming deposits on basin floor; western Hellas Planitia. Superposes its. Perhaps modified by compaction and Hto Hesperian transition outflow unit— Covers , eastern Lunae Outflow channel fluvial and debris-flow hummocky and troughed textures. units lHl, lHb, and HNb; gradational thermokarst Plains deposits in places dissected Planum, and canyons in Xanthe and deposits from catastrophic erosion of high- Variable daytime IR brightness. with units Av and AHv; superposed by by tens-of-kilometers-wide Margaritifer Terrae. Superposes units land rocks; islands of underlying bedrock Thickness <100 m in most places. unit mAl. Marked by wrinkle ridges in anabranching channel systems. AHv, lHt, eHh, eHv, eHt, lNh, mNh, Nhu, exposed (lat 37.44° N., long 111.17° E.; Hellas Planitia Relatively bright in nighttime IR and eNh; gradational with unit Ht; over- localities 3, 5, 41) in . Meters to at least lain by unit lHl lHb Late Hesperian basin unit—Plains- Covers central Hellas Planitia. Ice-rich eolian, lacustrine, and (or) volca- tens of meters thick. (lat 19.33° N., forming deposits on basin floor. Superposes units eHb, HNb, and lNv; nic air-fall deposits. Margins eroded and long 326.45° E.— Pathfinder Finely layered in places. Hundreds embayed by unit eAb. Complex, rugged back-wasted landing site; locality 12) of meters thick. (lat –40.80° N., surface marked by scarps and ridges; HNt Hesperian and Noachian transition Occurs adjacent to Noachian high- Noachian impact , sediments, and long 64.00° E.; locality 39) largely bounded by marginal scarp unit—Knobs, mesas, and inter- land materials along highland/lowland volcanic deposits with intervening aprons eHb Early Hesperian basin unit—Plains- Covers eastern margins of Hellas Basin fill of eolian, lacustrine, and (or) vol- vening aprons and plains. May be boundary except in lowlands east of of Hesperian mass-wasted materials. forming deposit. Several hundred Planitia. Superposes units HNb, lNh, canic origin. Modified by fluvial dissection. tens to hundreds of meters thick. Elysium rise and near Acidalia Mensa. Tectonically contracted meters thick along contact with lNv, and mNh; gradational with unit Tectonically contracted (lat 10.96° N., long 111.71° E.; Noachian part gradational with units unit HNb. (lat –37.95° N., long HNhu; overlain by unit lHb. Marked by locality 18) eNh, mNh, mNhm, lNh, Nve, and 78.84° E.; locality 44) crosscutting systems of wrinkle ridges Noachian part of ANa. Hesperian part and local valleys superposes units lNv, Nve, Nhe, Nhu, mNh, mNhm, and eNh; gradational HNb Hesperian and Noachian basin Forms Argyre and western Hellas Basin fill of eolian, lacustrine, and (or) with units eHt, eHh, Htu, Hve, and unit—Low-lying, plains-forming Planitiae. Embays units mNh, mNhm, volcanic origin. Tectonically contracted. Amazonian part of ANa; overlain by deposit. Relatively low daytime and eNhm; gradational with unit lNv; Sinuous ridges in interpreted units eHv, lHt, lHl, lHvf, AHtu, AHv, AHi, IR brightness in Hellas Planitia. overlain by units eHb, lHb, and eAb. as inverted fluvial landforms or eskers Av, mAl, lAv, and lAvf. Marked by pre- Thickness at least hundreds of Marked by wrinkle ridges and sinuous dominantly north-south-oriented wrinkle meters. (lat –33.53° N., long ridges ridges 59.53° E.; locality 40) HIGHLAND UNITS VOLCANIC UNITS [Materials forming densely cratered midland and highland areas (generally ~3,000 m to 5,000 m in surface elevation, down to less than [Lava flows and pyroclastic deposits forming volcanoes. Flow fields erupted from fissures and centralized vents; may include local –6,000 m in Hellas Planitia; high kilometer-scale surface roughness). Dominated by complex admixtures of impact, sedimentary, and pyroclastic deposits. Most occurrences are likely basaltic, based on rheologic properties estimated from morphologic measurements. volcanic rocks] Lava plains display low kilometer-scale surface roughness] HNhu Hesperian and Noachian highland Occurs on , in some Undifferentiated, friable (likely fine grained) lAv Late Amazonian volcanic unit— Covers , southern Largely unmodified flood , includ- undivided unit—Mound form- highland craters, and east of Hellas sedimentary, volcanic, and impact rocks. Planar deposits containing lobate Elysium Planitia, , periph- ing lava channels and other morphologies; ing. Light toned in visible images. Planitia. Superposes units eHh, lNh Altered by weathering scarps that extend hundreds to ery of Olympus Mons, and northeast of sourced from fissures and shields Layered. Hundreds of meters to (except gradational east of Hellas more than 1,000 km; sinuous . Superposes units Aa, several kilometers thick. (lat 5.97° Planitia), mNh, eNh, and eNhm; troughs, ridges, and platy textures Av, AHv, AHtu, AHi, lHv, lHl, lHt, Htu, N., long 2.33° E.; locality 24) gradational with unit eHb; overlain by common; low-relief, shield-like eHv, eHt, eHh, HNt, lNh; gradational units eHv and ANa (Amazonian part). edifices rare. Meters to tens of with unit lAvf and youngest parts of Includes hydrated sulfate spectral meters thick. (lat 26.27° N., long units Ave and AHv. Impact craters and signatures 192.67° E.; localities 9, 21) tectonic features sparse. Contains local roughness and albedo variations Nhu Noachian highland undivided unit— Occurs in Valles Marineris walls; in Undifferentiated friable sedimentary, impact, Forms canyon walls and some eastern Thaumasia and Malea Plana; and and volcanic materials. Tectonically con- lAvf Late Amazonian volcanic field Occurs in central parts of Tharsis rise Largely unmodified lava flows and vents; high plains and channel floors. along Kasei, Ares, and . tracted in places unit—Flows each typically tens and at Fossae. Superposes vents and flows not differentiated at map Layered. Hundreds of meters to Gradational with units lNh, lNv, mNh, of kilometers long extending units Aa, lHv, eHv, HNt, and most of scale several kilometers thick in expo- and eNh; overlain by units eHh, eHv, from shields and fissure vents as AHv; gradational with unit lAv and sures. (lat –25.80° N., long 288.53° eHt, Hp, Htu, Ht, Hto, HNt (Hesperian much as tens of kilometers across. youngest parts of units Ave and AHv. E.; locality 37) part), lHv, lHt, AHv, and Aa. Marked in Meters to at least tens of meters Impact craters and tectonic features places by wrinkle ridges and valleys thick. (lat –2.13° N., long 253.85° E.) sparse eHh Early Hesperian highland unit— Occurs on plateaus surrounding Tharsis Undifferentiated impact, volcanic, eolian, Av Amazonian volcanic unit—Rugged, Covers eastern Utopia and northern Lava and perhaps volcaniclastic flows from High plains-forming, relatively rise and in scattered highland lows. fluvial/lacustrine materials. Locally degraded hummocky, and pitted fields of Amazonis Planitiae. Superposes units and unknown source north- smooth outcrops extending hun- Superposes units lNh, lNv, Nhu, mNh, and (or) deformed irregular, poorly defined flows lHl and HNt and adjacent parts of unit west of Olympus Mons dreds of kilometers. May be hun- mNhm, eNh, and eNhm; gradational forming plains hundreds to more AHv; gradational with unit eAb; overlain dreds of meters thick. (lat 15.88° with units eHv and HNt (Hesperian part); than 1,000 km across. Tens of by units lAv, mAl, and Aa northwest of N., long 293.44° E.) overlain by units HNhu (in Schiaparelli meters or more thick. (lat 34.82° Olympus Mons. Subdued wrinkle ridges crater), Hto, lHv, lHvf, lHt, AHv, Aa, N., long 135.11° E.; locality 4) and lAv. Knobby, wrinkle-ridged, and dissected in places AHv Amazonian and Hesperian volcanic Forms bulk of the Tharsis and Elysium Flood lavas and large lava flows, undifferen- unit—Stacked, gently sloping rises. Locally, superposes units lHl, Hve, tiated, sourced from regional fissure and vent lNh Late Noachian highland unit— Occurs commonly in highland depres- Undifferentiated impact, volcanic, flu- lobate flows meters to tens of Ht, eHh, eHt, HNt, lNh, mNh, Nhu, and systems. Highly variable ages of individual Mostly plains forming, rugged in sions, as well as sparsely in higher-ele- vial, and basin material. Lightly to heavily meters thick and hundreds of kilo- eNh; gradational or interfingering with flows, although generally younger in central places. May be hundreds of meters vation parts of the lowlands. Superposes degraded and (or) deformed meters long. Variable daytime IR units lAvf, Ave, eAb, AHtu, lHt, lHvf, lHv, parts of Tharsis rise thick. (lat –20.74° N., long 354.35° units mNh, mNhm, eNh, and eNhm; brightness in places. Cumulative and eHv; overlain by units Av, mAl, lAa, E.; localities 13, 34, 35) gradational with units lNv, Nhu and HNt thicknesses reach hundreds of and lAv. Low crater density in central and ANa (Noachian parts); overlain by meters to several kilometers. part of Tharsis rise, moderate density units HNhu, eHv, eHh, eHt, eHb, Hp, (lat –22.76° N., long 242.33° E.) elsewhere Ht, Hto, lHl, lHv, lHvf, AHv, Apu, Aa, and lAv. Locally marked by grabens or lHv Late Hesperian volcanic unit— Distributed occurrence in Tharsis Flood lavas and large lava flows, undifferen- wrinkle ridges Lobate flows, meters to tens of region, southwestern Hesperia Planum, tiated, sourced from regional fissure and vent meters thick and tens to hundreds and . Superposes units systems mNh Middle Noachian highland unit— Extensive in the equatorial to southern Undifferentiated impact, volcanic, fluvial, of kilometers long; forms patches eHv, eHh, lNh, Nhu, Nhe, Nve, mNh, Uneven to rolling topography; highlands. Superposes units eNh and and basin materials. Moderately to heavily hundreds to more than a thou- eNh, and eNhm; gradational with units high-relief outcrops that extend eNhm; gradational with units mNhm, degraded sand kilometers across. Variable lHvf and Hve; overlain by units AHv, hundreds to thousands of kilome- Nhu, Nhe, Nve, and HNt and ANa daytime IR brightness in places. AHtu, ANa (Amazonian part), Aa, lAv, ters. Commonly layered in crater (Noachian parts); overlain by units lNh, Hundreds of meters or more total and lAvf. Largest patch in walls. May be hundreds of meters lNv, HNt (Hesperian part), HNhu, HNb, thickness. (lat –18.84° N., long region deeply dissected by troughs to more than a kilometer thick. eHb, eHv, eHh, eHt, Hp, Ht, Hto, Htu, 256.12° E.; localities 17, 29) and grabens of and (lat –47.17° N., long 349.33° E.; lHl, lHv, lHvf, ANa, AHtu, AHv, Apu, mAl, Noctis Fossae localities 7, 14, 19, 20, 22, 23, 31) and lAv. Heavily cratered and marked by locally dense valleys, grabens, and lHvf Late Hesperian volcanic field unit— Distributed occurrence in Syria Planum, Volcanoes and lava flows wrinkle ridges Patches hundreds of kilometers western , southwest of across of lobate flows typically Ceraunius Fossae, western Elysium eNh Early Noachian highland unit— Covers large parts of equatorial and Undifferentiated impact, volcanic, fluvial, meters thick and tens of kilometers Mons, and Orcus Patera. Superposes Rugged, very high relief outcrops southern highlands but sparse sur- and basin materials. Heavily degraded; tec- long emanating from low shields units eHh, HNt, lNh, mNh; gradational extending hundreds of kilometers. rounding Argyre basin, in , tonically deformed in places and fissure vents kilometers to tens or interfingers with units lHv, Hve, and Thickness commonly exceeds a and near highland/lowland boundary. of kilometers across. Hundreds AHv; overlain by unit ANa (Amazonian few kilometers but ill-defined. Gradational with units HNt (Noachian of meters or more total thickness. part). Locally modified by troughs and (lat –20.74° N., long 354.35° E; part), Nhu, Nhe, Nve, mNhm, and eNhm; (lat –12.31° N., long 257.63° E.) fissures localities 33, 36) overlain by mNh, lNh, lNv, HNhu, HNt (Hesperian part), eHv, lHv, lHt, Hp, Hto, eHv Early Hesperian volcanic unit— High plains within and near Tharsis Flood lavas, undifferentiated, sourced AHv, AHtu, AHi, Apu. Densely cratered; Planar deposits meters to tens of rise, Syrtis Major and Hesperia Plana, from regional fissure and vent systems. marked by broad, linear and irregular meters thick and tens to hundreds and crater. Superposes units Tectonically contracted scarps and ridges of kilometers across; lobate scarps HNt, HNhu, lNv, lNh, Nhu, Nhe, Nve, common. Variable daytime IR mNh, mNhm, eNh, and eNhm; grada- Nhe Noachian highland edifice unit— Occurs in southern highlands mostly lat Mainly undifferentiated, degraded volcanic brightness in places. Hundreds of tional with units eHt, eHh, Ht, and Hve; Irregular edifices marked by 30° to 70° S., especially south of Tharsis materials. Heavily degraded and tectonically meters or more total thickness. overlain by units Hto, lHv, lHt, lHl, AHv, troughs and peaks. As much as a region. Gradational with units HNt, lNh, modified (lat –25.34° N., long 279.97° E.; AHtu, lAv, and lAvf. Marked by wrinkle few kilometers thick. (lat –34.72° mNh and eNh; overlain by units lNh, localities 38, 42) ridges N., long 214.85° E.) lNv, HNt (Hesperian part), eHv, lHv, and AHv. Densely cratered and marked by INv Late Noachian volcanic unit—Planar Occurs in Malea and Thaumasia Plana, Degraded lava and volcaniclastic flows. scarps and ridges deposits meters to tens of meters Icaria Fossae area, and east of Hellas Tectonically contracted thick and tens to hundreds of kilo- Planitia. Superposes units Nhe, mNh, mNhm Middle Noachian highland massif Surrounds Argyre and part of Isidis Ancient, degraded crustal rocks uplifted by meters across; lobate scarps sparse eNh, and eNhm; gradational with units unit—High-relief massifs tens Planitiae. Gradational with units mNh, large, basin-forming impacts. Dissected by and indistinct. Variable daytime lNh, HNb, Nhu, and Nve; overlain by of kilometers across separated by eNh, and HNt (Noachian part); overlain basin-related structures and erosional IR brightness in places. Hundreds units eHv, eHh, eHb, lHb, Hp, HNt broad linear troughs and valleys. by units lNh, HNb, HNt (Hesperian part), valleys of meters or more total thickness. (Hesperian part), AHv, and Aa. Includes Kilometers thick. (lat –44.48° N., eHh, eHt, eHv, lHt, and lHl. Heavily cra- (lat –55.89° N., long 67.99° E.; some degraded craters; marked by wrin- long 307.54° E.) tered; dissected by grabens and valleys localities 46, 47) kle ridges in places

Ave Amazonian volcanic edifice—Shield- Forms Olympus, Alba, Ascraeus, Volcanic edifices composed of lava flows eNhm Early Noachian highland massif Forms annulus around most of Hellas Primitive, degraded crustal rocks uplifted by like edifices hundreds of kilo- Pavonis, and Arsia Montes. Younger and possible volcaniclastic rocks. Deformed unit—Forms high-relief massifs Planitia. Gradational with units eNh and large, basin-forming impact. Dissected by meters across; made up of lobate part superposes units Aa and AHtu; by summit collapse from magma withdrawal tens of kilometers across separated ANa (Noachian part); overlain by units basin-related fault structures and erosional flows meters to tens of meters gradational with units lAvf, and AHv; and gravity spreading of flanks by broad linear troughs and val- mNh, lNh, lNv, HNb, HNhu, eHv, Hve, valleys thick and tens to hundreds of overlain by unit lAa. Deformed by leys. Kilometers thick. (lat –26.00° and lHv. Heavily cratered; dissected by kilometers across. Edifices several summit calderas tens to >100 km wide N., long 63.24° E.; localities 43, valleys in places to more than ten kilometers high. and circumferential scarp systems 45) (lat 18.89° N., long 225.86° E.)

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.