Preliminary bedrock geologic map of the Port Henry quadrangle, Essex County, New York, and Addison County, Vermont
<h1>Introduction </h1><p>The bedrock geology of the 7.5-minute Port Henry quadrangle consists of deformed and metamorphosed Mesoproterozoic gneisses of…
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ISSN 2331-1258 (online) ://doi.org/10.3133/ofr20261062 Any use of trade, firm, or product names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225; ://store.usgs.gov; 1-888-ASK-USGS (1-888-275-8747) Suggested citation: Valley, P.M., Parker, M., Walsh, G.J., Orndorff, R.C., Walton, M.S., Jr., and Crider, E.A., Jr., 2026, Preliminary bedrock geologic map of the Port Henry quadrangle, Essex County, New York, and Addison County, Vermont: U.S. Geological Survey Open-File Report 2026–1062, 1 sheet, scale 1:24,000, ://doi.org/10.3133/ofr20261062. Associated data for this publication: Valley, P.M., Parker, M., Walsh, G.J., Orndorff, R.C., Walton, M.S., Jr., and Crider, E.A., Jr., 2026, Database for the preliminary bedrock geologic map of the Port Henry quadrangle, Essex County, New York, and Addison County, Vermont: U.S. Geological Survey data release, ://doi.org/10.5066/P13HYFPM. 1U.S. Geological Survey. 2Yale University, New Haven, Conn., deceased. Preliminary Bedrock Geologic Map of the Port Henry Quadrangle, Essex County, New York, and Addison County, Vermont By Peter M. Valley,1 Mercer Parker,1 Gregory J. Walsh,1 Randall C. Orndorff,1 Matt S. Walton, Jr.,2 and E. Allen Crider, Jr.1 43°52’30” 44° 44°07’30” 44°15’ 73°37’30” 73°30’ 73°22’30” 73°15’ INDEX TO 7.5’ QUADRANGLES [Study area shown in red] SNAKE MOUNTAIN PORT HENRY VERGENNES WEST WESTPORT CROWN POINT BRIDPORT WITHERBEE EAGLE LAKE ELIZABETHTOWN Figure 1. Simplified geologic map of the Adirondacks, upstate New York, showing the location of the Port Henry quadrangle. Rocks in the Adirondack Lowlands are shown with lighter shades of the same colors as in the Highlands. Simplified from Rickard and others (1970) and Isachsen and Fisher (1970) with digital data from Dicken and others (2005). Inset map of the Grenville Province shows Mesoproterozoic inliers in northeastern North America; modified from Hibbard and others (2006). Abbreviation: CCSZ, Carthage-Colton shear zone. Undifferentiated rocks and sediments outside the Adirondacks Quaternary sediments Anorthosite-mangerite-charnockite-granite suite Leucogranitic (alaskitic) gneiss including the Lyon Mountain Granite Gneiss Biotite and (or) hornblende granitic gneiss, locally pyroxenic Charnockitic, mangeritic, granitic, syenitic gneiss with hornblende, pyroxene, and biotite; darkest shade indicates inequigranular texture including the Hawkeye Granite Gneiss from unit “” of Isachsen and Fisher (1970) EXPLANATION Anorthositic rocks Metagabbro Marble and calc-silicate rock Undifferentiated paragneiss and migmatite gneiss Amphibolite Tonalitic gneiss Fault Town Water bodies from U.S. Geological Survey National Hydrography Dataset Universal Transverse Mercator North American Datum of 1983 36 KILOMETERS 24 MILES QUEBEC NEW YORK VERMONT ONTARIO St. Lawrence River La ke
hamplain Lyon Mountain Port Henry Ticonderoga Plattsburgh Keene Glens Falls Carthage Lake Placid Hawkeye Marcy massif Adirondack Lowlands Adirondack Highlands h am p a n
Valle y SZ S Z Port Henry quadrangle Adirondack massif NY VT Grenville Province 43° 44° 45° 76° 75° 74° 73° DESCRIPTION OF MAP UNITS [Minerals are described in order of increasing abundance where hyphenated] HOLOCENE DEPOSITS Undifferentiated waste rock piles and tailings (Holocene)—Areas of filled land, iron slag, tailings, or mine dumps related to historic iron and graphite mines. The unit was mapped with lidar and ground observations QUATERNARY DEPOSITS Undifferentiated glacial deposits (Quaternary)—Large areas of glacial sediments covering bedrock in the western and southwestern parts of the Port Henry quadrangle in New York and in the Champlain Valley of Vermont and New York. Glacial sediments include lake sediments, terraces, beaches, glacial river deposits, deltas, outwash plains, and unconsolidated sand, gravel, or glacial till. Glacial deposits are mapped only in a preliminary way in parts of the quadrangle MESOZOIC FAULT ROCKS Silicified zone (Mesozoic)—Rusty sulfidic rock, brecciated and cemented by quartz; locally schistose. Outcrops are present within the town of Port Henry along a brittle fault, which separates the Potsdam Sandstone ( pt) from Proterozoic basement, and present approximately 1 kilometer (km) north of Craig Harbor along a brittle fault, which separates graphitic marble (Ym) from amphibolite (Ya) MESOZOIC IGNEOUS ROCKS Trachyte dike (Cretaceous)—Tan, very fine grained, aphanitic trachyte to microsyenite. Shown by blue strike and dip symbol only at one location along Route 9N in the northern part of the map. May correlate with rocks dated at 131.1±1.7 Ma (mega-annum) and exposed at Cannon Point approximately 20 km to the north (Bailey and others, 2016) PALEOZOIC SEDIMENTARY ROCKS Stony Point Formation (Upper Ordovician)—Dark gray to black, light gray to locally tan weathering, calcareous shale interbedded with dark-gray to black, thin-bedded, shaly limestone. The basal contact is placed at the transition from fossiliferous, thin-bedded limestone of the Glens Falls Limestone (Ogf) to thin-bedded shaly limestone interbedded with calcareous shale. The unit is well exposed along the eastern shores of Lake Champlain in Vermont from north of Chimney Point up to Potash Point. The contact is covered and is approximately located on the map. The contact between the Glens Falls Limestone and Stony Point Formation is gradational (Welby, 1961). The thickness of the unit is undetermined due to the lack of a complete section in the map area. Welby (1961) estimated the thickness of the unit at about 1,000 feet (ft) (305 m) in Vermont where the Stony Point Formation is overlain by the Iberville Formation (not exposed in this quadrangle) Glens Falls Limestone (Upper Ordovician)—Dark-gray to black, bluish-gray weathering, thin- to medium-bedded, fossiliferous, grainstone with argillaceous partings interbedded with dark-gray shaly limestone. The basal contact is placed at the transition from medium-bedded limestone of the Orwell Limestone (Oo) to the interbedded, thin-bedded limestones containing beds abundant in fragments of the trilobite Cryptolithus. The unit is well exposed along the shores of Lake Champlain at the Crown Point State Historic Site, New York. Thickness is estimated at 450 ft (137 m) Orwell Limestone (Upper Ordovician)—Dove-gray weathering, black to dark-gray, medium bedded, fine-grained limestone containing black chert nodules. Samples from the lower part of the formation contain conodonts of the Belodina compressa Biozone. The lower contact is best exposed at the Crown Point State Historic Site, New York, and is placed above the highest dolostone of the underlying Valcour Limestone (Ov). A quartz arenite, approximately 3–5 ft in thickness, occurs several feet above the contact with the Valcour Limestone throughout the map area. Thickness is estimated at 70 ft (21 m) Valcour Limestone (Upper Ordovician)—Dark to light-gray, thick-bedded, medium-grained limestone, dolomitic limestone, arenaceous dolostone, and dolostone. The dolostone weathers light brown. Burrows are common throughout the lower part of the formation. The unit is best exposed at the Crown Point State Historical Site, New York. The lower contact is not well exposed but is placed at the base of the lowest dolostone. Thickness is estimated at 80 ft (24 m) Crown Point Limestone (Upper and Middle Ordovician)— Medium-dark-gray, thin- to medium-bedded, coarse-grained fossiliferous limestone with very dark gray argillaceous partings and is dolomitic in places. Basal beds are very light gray weathering, medium- to dove-gray, thick-bedded mudstone limestone. Contains the diagnostic gastropod Maclurites. Upper beds contain quartz and feldspar sand grains. The contact with the underlying Providence Island Dolomite (Opi) is placed at the base of high-calcium mudstone overlying fetid dolostone. The upper part of the unit is best exposed at Crown Point State Historic Site, New York. Thickness is estimated at 175 ft (53 m) Providence Island Dolomite (Middle and Lower(?) Ordovician)— Tan and light-gray weathering, gray to light-gray, laminated dolostone with interbedded gray limestone, noncalcareous shale, and argillaceous partings. Has “beeswax-scored” and “butcherblock” surfaces on weathered surfaces. Samples for conodonts were barren. The lower contact is not exposed in the quadrangle. The unit is well exposed in Mullen Brook, west of County Highway 44, and along the western shores of Lake Champlain north of Stevenson Bay. Thickness is estimated at 200 ft (61 m) Cutting Dolomite (Lower Ordovician)—Light-gray to light-tan weathering, medium-gray to dark-olive-gray, thick-bedded, crystalline dolostone, sandy dolostone, and dolomitic sandstone. Well defined crossbedding in places. Weathered surfaces have “butcherblock” patterns. The lower contact is placed at the transition from massive, crystalline dolostone of the Whitehall Formation (O w) to a dolomitic, crossbedded quartz sand with sand grains weathering in relief. However, the Cutting Dolomite is fault bounded in the map area and the lower contact is not exposed. The conodont Rossodus manitouensis Biozone occurs within the unit. Thickness is estimated at 225 ft (69 m) Whitehall Formation (Lower Ordovician and Upper Cambrian)— Light- to brownish-gray and pinkish, thick-bedded to massive, medium to coarsely crystalline (sugary) dolostone with local sand and limestone interbeds and black chert nodules. Unit is siliceous in places with a fetid odor from fresh surfaces. Lower contact with the Ticonderoga Formation ( ti) is gradational and placed where sandy dolostone grades upward to dark-gray, crystalline dolostone of the Whitehall Formation. The Whitehall and Ticonderoga Formations are in fault contact in the map area and the stratigraphic contact is not exposed. Thickness is estimated at 250 ft (76 m) Ticonderoga Formation (Upper Cambrian)—Brownish-gray, yellowish-gray, buff to light-gray weathering, dark- to medium-gray, medium- to thick-bedded, cherty and sandy, fine- to medium-grained dolostone with quartzose dolostone and pebbly dolomitic sandstone interbedded with quartz sandstone. Chert occurs as black nodules. Sandy dolostone beds weather yellowish gray. Quartz grains are subrounded to rounded and frosted. Base of the unit is gradational and marked by decreasing sandstone of the Potsdam Sandstone ( pt) to dolomite and sandy dolomite of the Ticonderoga Formation and placed at the first significant dolostone beds. Locally, contains worm burrow trace-fossils. Thickness is estimated at 175 ft (53 m) Potsdam Sandstone (Upper and Middle(?) Cambrian)—Gray to greenish-gray, locally maroon, tan, or rusty weathering, poorly sorted, subangular to subrounded, coarse- to medium-grained, well-bedded sandstone, with coarse sandstone and pebble conglomerate near the base of the unit. Bedding thickness varies from meter- to decimeter-scale and is locally massive and crossbedded. Locally, recrystallizes to quartzite. Contains abundant ripple marks. The unit grades upwards from arkosic sandstone to quartz arenite interbedded with dolostone and dolomitic sandstone. The basal contact is an unconformity overlying Mesoproterozoic rocks. The bearing granitoids, and collectively refer to the unit as broadly charnockitic. Uranium-thorium-lead (U-Th-Pb) zircon geochronology in the Adirondack Mountains suggests a crystallization age for the charnockitic rocks at about 1,158 Ma (McLelland and others, 2004; Aleinikoff and others, 2021) Metagabbro (Mesoproterozoic)—Dark-green to black, dark-gray to tan, or rusty weathering, massive to weakly foliated, medium- to coarse-grained, equigranular, olivine-spinel-plagioclase-orthopyroxene- clinopyroxene metagabbro to metanorite with accessory ilmenite and magnetite. The unit takes on a salt and pepper appearance with increased deformation. The unit typically contains dark knots of concentrically zoned mafic phases and contains a metamorphic assemblage of plagioclase, clinopyroxene, orthopyroxene, biotite, ilmenite, hornblende, and garnet, developed as coronas around primary phases. Olivine is rare, but where present, forms the core of the corona. Corona mineralogy is complex and often incomplete, but the general sequence from core to rim is olivine (rare)- orthopyroxene-clinopyroxene/spinel symplectite-amphibole-garnet. There is a second set of coronas with ilmenite cores and amphibole/ biotite rims. The unit contains primary spinel clouded plagioclase, clinopyroxene, and rare olivine. Locally, the margins of the metagabbro bodies contain a zone of foliated migmatite or mylonitic amphibolite mapped separately as unit Ya; the marginal amphibolite is interpreted as deformed, migmatitic, and hydrated equivalents of the metagabbro core (Regan and others, 2011). The metagabbro underlies resistant knobs and is well exposed in many places including the Cheever mine and the Moore Mountain dome. The gabbro forms the footwall to the ore at the Cheever and Pilfershire mines and is the host rock to the ore at the Craig Harbor mine Anorthosite, leucogabbro, and gabbroic gneiss (Mesoproterozoic)— White to bluish-gray weathering, or salt and pepper, leucogabbro and leucogabbroic gneiss, containing subordinate dark gabbroic gneiss and syenitic gneiss. Anorthosite is rare in the Port Henry quadrangle. Texturally, the rock varies from undeformed with magmatic textures to gneissic that locally exhibits mylonitic to protomylonitic strain. Locally, contains areas of intrusion breccia with plutonic or tectonic fragments of anorthositic rock entrained in leucogabbro or leucogabbro gneiss. Prior to the adoption of the International Union of Geological Sciences (IUGS) classification system, “leucogabbro” was previously and widely referred to as “gabbroic anorthosite.” We apply the IUGS nomenclature (Streckeisen, 1976) for leucogabbro as a rock containing 10–35 percent mafic minerals, which differs from Buddington’s (1939) local usage of gabbroic anorthosite as a rock containing 10–22.5 percent mafic minerals. Unit contains primary orthopyroxene and clinopyroxene and metamorphic hornblende, biotite, and garnet. Mafic mineral content of leucogabbro is variable but approximately ranges between 10–30 modal percent. Accessory minerals include ilmenite, magnetite, apatite, and titanite. Locally, contains coarse andesine megacrysts deformed into augen, and decimeter-scale lenses of gabbroic gneiss, which may also contain coarse andesine megacrysts and augen. Gabbroic gneiss contains up to 40 modal percent coarse andesine xenocrysts, and a matrix of clinopyroxene, orthopyroxene, biotite, hornblende, plagioclase, garnet, and ilmenite. Accessory phases include apatite, quartz, and magnetite. Gabbroic gneiss is interlayered at a variety of scales including submeter layering and meter-scale boudins that locally do not permit separation at 1:24,000 scale. Well exposed on Cheney Mountain, and in the Moore Mountain dome where the unit forms the core of the dome. The unit predates all other units in the AMCG suite. Traditionally interpreted to be a large chill margin on the border of the Marcy massif (Cushing, 1917; Miller, 1918, 1919). Informally referred to as “Whiteface type” anorthosite (Kemp, 1898; Miller, 1918, 1919) Granitic augen gneiss (Mesoproterozoic)—Gray to tan or orange, locally light-pink, dark-gray to tan or orange to brick red-weathering, well-foliated, inequigranular, megacrystic granite gneiss with K-feldspar (perthite-microperthite) augen (1–5 cm) in a matrix of quartz, plagioclase, K-feldspar, biotite, and locally abundant garnet. The unit contains accessory epidote, zircon, and allanite, and contains lesser amounts of variably foliated, layer-parallel pegmatitic granite gneiss with quartz, mesoperthite, and accessory epidote. Because of its characteristic texture and resistant weathering, the unit is relatively easy to recognize and map in the field. It occurs as highly deformed, foliation-parallel, thin sill-like bodies. The unit is only present within the Cheney Mountain shear zone in a large exposure on the southeast side of Cheney Mountain, with smaller meter-scale exposures between Cheney Mountain and Walton Mountain but could not be separated at 1:24,000 scale. The smaller outcrops are associated with calc-silicate marble and Ylg. Regan and others (2019) report a sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon age of 1,185±11 Ma from the Eagle Lake quadrangle MESOPROTEROZOIC METASEDIMENTARY AND METAIGNEOUS ROCKS Grenville Complex [In the Port Henry quadrangle, there is a general ordering of metasedimentary rocks. It is not clear if this ordering is tectonic, stratigraphic, or a combination of both. The units below are listed (where possible) from top to bottom as the map pattern dictates] Migmatitic biotite gneiss member (Mesoproterozoic)—Gray to dark-gray, dark-gray to black and white banded, light-gray weathering, well-foliated, migmatitic, medium-grained, biotite-K- feldspar-quartz-plagioclase paragneiss with locally undifferentiated amphibolite and calc-silicate rock. The unit is well layered and varies from an equigranular quartz-feldspar gneiss to a well-layered biotite-rich migmatite. Locally, the unit preserves an S1 foliation that is parallel to the compositional layering. Accessory phases include hornblende, garnet, sillimanite, magnetite, diopside, epidote, apatite, zircon, allanite, and sulfides. Sedimentary layering is largely destroyed due to metamorphism and tectonism, but local compositional banding, especially of interlayered light-green calc-silicate rocks, is likely a remnant of original bedding. The unit is locally interlayered on the meter-scale with fine-grained amphibolite. Leucosome occurs as pegmatitic segregations, dikes, and sills. Nonmigmatitic varieties contain little biotite, and consist mostly of K-feldspar, quartz, and plagioclase. Locally, the unit is rusty and sulfidic. The unit is well exposed in the southern part of the Port Henry quadrangle on the west side of Coot Hill and along route 9N northeast of Coot Hill. A smaller exposure is mapped north of Port Henry near Mullen Bay but is absent in the large central part of the map. The unit forms the base of the Great Unconformity exposed in Mullen Brook and at Mullen Bay Calc-silicate marble member (Mesoproterozoic)—Pale-green, white and gray to tan and earthy yellowish-brown or rusty weathering, medium-grained, epidote-tremolite-quartz-diopside calc-silicate gneiss to granofels. Diopside is the dominant calc-silicate mineral and gives the rock a green and white spotted appearance on fresh surfaces. “Ant-hole” weathering is common and diagnostic especially in outcrops where diopside is lacking or poorly exposed in the woods. The unit contains accessory plagioclase, tremolite-actinolite, magnetite, chlorite, apatite, and graphite, and often has a retrograde mineral assemblage, where plagioclase is saussuritized and diopside is replaced by tremolite-actinolite and epidote. One sample along Pilfershire Road consists of diopside and scapolite. In the Port Henry quadrangle, the majority of Ycs occurs above Ysi. In the western part of the map area, Ycs is interlayered with Ysi. Smaller outcrops occur within the graphitic marble (Ym) and as thin 1- to 6-m-thick layers along the northeastern part of the Cheney Mountain shear zone near Walton Mountain Rusty garnet-sillimanite gneiss member (Mesoproterozoic)— Typically weathers rusty brown but varies locally from gray to dark-gray and tan, white to tan-gray, well-foliated, migmatitic, garnet-sillimanite-K-feldspar-plagioclase-quartz paragneiss with variable amounts of graphite and biotite. Locally, the unit is sulfidic and very rusty weathering. Accessory phases include pyrite, monazite, zircon, apatite, xenotime, allanite, epidote, and ilmenite. Paragneiss contains undifferentiated interlayered quartzite, calc-silicate gneiss, and minor marble and amphibolite. Contains abundant layer-parallel, locally garnet- and (or) graphite-rich pegmatite and garnetite as variably dismembered boudins and sill-like intrusions. Leucosome occurs as pegmatitic segregations, dikes, and sills. Layering varies in thickness but is predominately on the order of meters to decimeters except where interleaved with calc-silicate gneiss and quartzite, where it is layered on the cm- to decimeter-scale. Referred to as khondalite (McLelland and others, 1988) or kinzigite (Walton, 1966). The unit is interpreted as metamorphosed interbedded psammitic to pelitic rocks that underwent partial melting. Locally, coarse garnet (up to 2 cm) comprises up to 50 percent of the rock. Garnet is typically pink and contains abundant quartz inclusions and is locally “book-shelved” and partially replaced by biotite or sillimanite. Although tectonic and metamorphic in origin, large exposures of this unit exhibit modal variations in biotite, garnet, and quartz at the cm scale, which is interpreted as a pseudostratigraphy. The unit is well exposed immediately north of the town of Port Henry along Mill Brook and along the power line between Switchback and Cheney Road. Graphite was prospected in the unit on the hill immediately north of Mill Brook. The unit was historically mined for graphite south of the Port Henry quadrangle near Ticonderoga, New York Amphibolite gneiss member (Mesoproterozoic)—Massive to well-foliated, dark-green to black, gray to rusty weathering, medium-grained, amphibolite consisting of hornblende-plagioclase gneiss or pyroxene-hornblende-plagioclase gneiss. Where pyroxene is present, clinopyroxene is always part of the assemblage with or without orthopyroxene. Garnet is common and abundant in many places. Locally, the unit contains biotite and sulfides; microcline and quartz are present locally where the rock is migmatitic. Unit Ya is interlayered within units Ybg, Ysi, Ycs, Yqt, and Ym, and the layering is interpreted as primary. The amphibolite locally occurs as xenoliths or screens in units Ylg and Yhg, but its relationship to the sedimentary stratigraphy is uncertain. Amphibolite gneiss also occurs along the margins of metagabbro bodies, but it is not mapped separately in most places at the scale of the map and is of a different origin. The amphibolite is locally interlayered with marble and calc-silicate gneiss at a scale too small to map. The unit is well exposed at Burns Mountain and Colligan Hill with smaller mappable layers within unit Ym Quartzite and quartzofeldspathic gneiss (Mesoproterozoic)— Light-gray to tan, variably rusty weathering quartzite, feldspathic quartzite, and quartzofeldspathic biotite gneiss and minor rusty schist. Varying amounts of garnet-sillimanite-plagioclase-quartz and minor K-feldspar and magnetite. Quartzite is massive or thickly layered and may contain minor amounts of garnet and sillimanite. In some outcrops, feldspars weather in relief, giving the rock a rough texture. Quartzofeldspathic gneiss is difficult to distinguish from unit Ylg in lichen covered outcrops, due to similar weathering style and the presence of magnetite. The unit is exposed in narrow bands north and south of Mill Brook and within unit Ym, north of Port Henry along Route 9 Two-mica granite gneiss (Mesoproterozoic)—White to gray weathering with tan staining, biotite-muscovite-garnet-plagioclase- K-feldspar-quartz gneiss±hornblende, magnetite, and sulfides. Biotite is highly variable. Locally, the unit consists of only quartz-feldspar- garnet±magnetite. Appears massive and blocky and the foliation is not well developed. The unit is exposed south of the Cheever ore body and is hosted by unit Ym, and on one small hill immediately south of Elk Inn Road. It is the only unit mapped that has muscovite consistently in the mineral assemblage. The unit is likely to be part of the sedimentary package and not related to the AMCG suite Graphitic marble member (Mesoproterozoic)—White to gray, and dark-gray, commonly tan to earthy yellowish-brown or rusty weathering, poorly exposed, deeply weathered, coarse-grained graphitic marble, minor rusty schist, quartzite, and calc-silicate marble. Amphibolite layers, pods, and blocks are ubiquitous. The unit contains appreciable amounts of pegmatite too small to map separately. The composition and modal mineralogy vary within individual exposures, and the unit is well-layered to massive. Marble is coarse grained, well annealed, and contains coarse (up 1 cm) quartz in recrystallized masses that compose <15 percent of the rock, but weather in high relief. The amount of flake graphite (up to 2 cm) varies between to 30 percent and is variable on the cm- to m-scale. Varying accessory phases include graphite, scapolite, phlogopite-biotite, plagioclase, microcline, hornblende, wollastonite, olivine, diopside, garnet, hornblende, molybdenite, tremolite, pyrite, tourmaline, and titanite. Faults and fractures locally contain white to light-gray asbestiform fibrous minerals (Walsh and others, 2022). Alteration products of silicates include chlorite, talc, tremolite, actinolite, serpentine as asbestiform chrysotile-antigorite, sericite, and zoisite. Pale-green to gray, rusty weathering, calc-silicate gneiss is layered on the cm- to decimeter-scale, and consists of varying proportions of diopside, talc, tremolite, quartz, and dolomite with accessory tourmaline, titanite, and pyrite. Thick recrystallized marble horizons may contain foliated and locally folded tectonic rafts of adjacent units, especially quartzite, amphibolite, and paragneiss. The unit preserves rare F1 folds and exhibits distinctive alternating resistant and highly recessive layers due to varying amounts of quartz and or calc-silicate minerals. The unit forms the base of the Grenville Complex in Port Henry and is in contact with the underlying AMCG suite, typically unit Ylg. Graphitic marble forms large cliffs along Lake Champlain north of Port Henry. Karst is locally present north of Port Henry. The unit covers a wide area north of Port Henry and forms the base of the hanging wall in the Cheney Mountain shear zone. It is common to find Ylg intruding the unit where its base is exposed EXPLANATION OF MAP SYMBOLS Contact—Approximately located, dotted where concealed, queried where uncertain Outcrops—Areas of exposed bedrock or closely spaced contiguous bedrock exposures examined in this study; some areas are enlarged to show location FAULTS [Approximately located; dotted where concealed. Listed from youngest to oldest] Brittle fault (Mesozoic to Paleozoic)—Steeply dipping; dotted where concealed; queried where uncertain. Locally characterized by cataclasite, breccia, and veins; U, upthrown side; D, downthrown side Ductile shear zone (Mesoproterozoic)—Characterized by penetrative mylonitic textures with quartz ribbons and deformed feldspar, amphibole, and pyroxene depending on lithology; arrows indicate relative motion; dotted where concealed. Shear zones are characterized by upper amphibolite facies metamorphic assemblages that are syn- to post-pegmatite emplacement. The Cheney Mountain shear zone, named herein, is a major northwest-southeast trending shear zone. Similar shear zones occur at the outcrop scale and are shown with D4 shear zone symbology Strike and dip of D4 shear bands—Includes axial surface of related minor folds; locally filled with pegmatite (Yp) Inclined, sinistral Inclined, dextral FOLDS [Symbols show trace of axial surface and direction of dip of limbs; location is known] Axial trace of F3 fold (Mesoproterozoic) Synform Dome MINOR FOLDS [Folds in Mesoproterozoic rocks; listed from youngest to oldest] Strike and dip of inclined F4 axial surface—Includes minor open fold or plane of boudinage; locally filled with pegmatite (Yp) Strike and dip of inclined F3 axial surface—Includes minor open to tight fold; locally filled with pegmatite (Yp) and rarely expressed as a nonpenetrative cleavage; arrow, when present, shows bearing and plunge of hinge line of fold Strike and dip of inclined F2 axial surface—Includes minor tight to isoclinal fold; locally filled with pegmatite (Yp); arrow, when present, shows bearing and plunge of hinge line of fold PLANAR FEATURES [Symbols may be combined; point of intersection shows location of measurement; listed from youngest to oldest] Strike of vertical Mesozoic trachyte dike Strike and dip of inclined cleavage in Paleozoic rocks Strike and dip of bedding in Paleozoic rocks Inclined Vertical Strike and dip of mafic dike (Zd) (Ediacaran) Inclined Vertical Strike and dip of quartz vein (Mesoproterozoic)—Locally common in leucogranite (Ylg); may contain accessory feldspar, epidote, magnetite, hematite, and calcite. Quartz-carbonate veins occur in the Paleozoic rocks but were not mapped Inclined Vertical Strike and dip of pegmatite dike or sill (Yp) (Mesoproterozoic) Inclined Vertical No strike and dip measurement Strike and dip of inclined leucogranite sill (Ylg) (Mesoproterozoic) Strike and dip of S2 gneissosity (Mesoproterozoic)—The most conspicuous foliation in the Mesoproterozoic rocks; includes the layer parallel foliation in the Lyon Mountain Granite Gneiss (Ylg) Inclined Vertical Strike and dip of inclined S1 gneissosity (Mesoproterozoic)— Foliation is parallel to compositional banding in paragneiss. The S1 foliation predates the Lyon Mountain Granite Gneiss (Ylg) LINEAR FEATURES [Symbols may be combined; point of intersection shows location of measurement; listed from youngest to oldest] Bearing and plunge of F3 minor fold axis—Associated with dome-stage folds, locally parallel to aligned nodules of sillimanite and quartz Bearing and plunge of intersection lineation—Intersection lineation between D2 gneissosity and younger jointing due to inherited structural weakness along the edge of, and parallel to, the L2 mineral lineation Bearing and plunge of F2 minor fold axis—Fold axis of tight, isoclinal, or rootless fold associated with S2 Bearing and plunge of L2 mineral lineation—Aggregate lineation or grain lineation associated with the S2 foliation; consists of quartz, biotite, hornblende, pyroxene, or sillimanite OTHER FEATURES Abandoned quarry, mine, or prospect—Abandoned quarries occur in Mesoproterozoic marble and Paleozoic carbonate and clastic rocks. Abandoned iron mines occur in the Mesoproterozoic Lyon Mountain Granite Gneiss (Ylg) and metagrabbro (Ygb) Quarry Mine Prospect Gamma radiation point—Shows location where a portable radiation detector measured more than two times the background radiation Abandoned narrow gauge railroad—Abandoned railbed formerly used for hauling ore and materials between mines and various processing facilities in Port Henry INTRODUCTION The bedrock geology of the 7.5-minute Port Henry quadrangle consists of deformed and metamorphosed Mesoproterozoic gneisses of the Adirondack Highlands unconformably overlain by weakly deformed lower Paleozoic sedimentary rocks of the Champlain Valley (fig. 1). The Mesoproterozoic rocks occur on the eastern edge of the Adirondack Highlands and represent an extension of the Grenville Province of Laurentia (fig. 1, inset). Mesoproterozoic paragneiss, marble, and amphibolite hosted the emplacement of an anorthosite-mangerite- charnockite-granite (AMCG) suite, now exposed mostly as orthogneiss, at approximately 1.18–1.15 Ga (giga-annum). In the Port Henry quadrangle, the AMCG metaigneous rocks (Yhg, Ygb, Yanw) intruded older, mostly metasedimentary rocks of the Grenville Complex during the middle to late Shawinigan orogeny (~1,160–1,150 Ma [mega-annum]). All rocks were subsequently metamorphosed to upper amphibolite to granulite facies conditions during the 1,080–1,050 Ma Ottawan orogeny. New mapping reveals four periods of deformation: (1) D1 produced rarely preserved isoclinal folds in the paragneiss and marble and predates AMCG magmatism. (2) Subsequent D2 deformation produced the dominant gneissic fabric preserved in the rock, recumbent folding, and deformed all the Proterozoic units in the map area. Syn- to late-D2 felsic magmatism resulted in the regionally extensive Lyon Mountain Granite Gneiss, which hosts numerous magnetite ore bodies. (3) Mylonitic extensional shear zones and core complex formation marked the beginning of D3 deformation. Protracted D3 deformation resulted in F3 upright folding, dome and basin formation, pegmatite intrusion, reactivation of the S2 foliation, partial melting, metamorphism, metasomatism, iron-ore remobilization, and intrusion of magnetite-bearing pegmatite both as layer-parallel sills and crosscutting dikes. (4) D4 created northeast- and northwest-trending local high-grade ductile shear zones and boudinage, northwest-trending regional kilometer (km)-wide ductile shear zones, and crosscutting granitic pegmatite dikes. The development of the late-stage regional shear zones (D4) was likely due to the continuation of extensional doming and uplift from upper amphibolite facies conditions at the end of the Ottawan orogeny. The majority of iron-ore deposits in the Port Henry and adjacent Witherbee quadrangles are in the hanging wall of these extensional shear zones. In the Port Henry quadrangle, the km-wide Cheney Mountain shear zone is the result of D4 deformation. Kilometer-scale lineaments readily observed in lidar data are Ediacaran mafic dikes and Phanerozoic brittle faults. The Paleozoic rocks are part of the Early Cambrian to Late Ordovician carbonate bank on the ancient margin of Laurentia. The approximately 1-km-thick Cambrian to Ordovician stratigraphy records a transition from synrift clastics to passive-margin peritidal carbonate buildups to gradually deeper-water subtidal- to shelf-carbonates during foreland basin development associated with the Taconic orogeny. The Paleozoic rocks are weakly folded and block faulted. Large areas of the Champlain Valley are covered by undifferentiated glacial deposits, some of which contain mapped landslides. The map also shows waste rock piles and tailings from historical mining operations. This study was undertaken to improve our understanding of the bedrock geology in the Adirondack Highlands, establish a modern framework for 1:24,000-scale bedrock geologic mapping in the Adirondacks, provide a context for historical iron mines in the eastern Adirondacks, and update the stratigraphy of the Champlain Valley in New York and Vermont. This Open-File Report includes a bedrock geologic map; a description of map units; a correlation of map units; and a geographic information system database (Valley and others, 2026) that includes bedrock geologic units, faults, outcrops, and structural geologic information. ACKNOWLEDGMENTS We thank Marian Lupulescu (New York State Museum, deceased) for the many years of help and depth of knowledge on magnetite mines of the eastern Adirondacks. We also thank Jessica Matthews (U.S. Geological Survey) and Chris Kopf (retired) for their assistance during fieldwork; Kathleen Bonk (New York State Museum, New York State Geological Survey) who kindly answered multiple requests for access to archival manuscript maps that made unpublished manuscripts available that helped define the map units in the Port Henry quadrangle; and Lyme Adirondack Timberlands that allowed entry to their private forest lands via annual written permits, which provided essential access to much of the northern area of the map. REFERENCES CITED Aleinikoff, J.N., Walsh, G.J., and McAleer, R.J., 2021, New interpretations of the ages and origins of the Hawkeye Granite Gneiss and Lyon Mountain Granite Gneiss, Adirondack Mountains, NY—Implications for the nature and timing of Mesoproterozoic plutonism, metamorphism, and deformation: Precambrian Research, v. 358, no. 106112. 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[Also available at ://.usgs.gov/Prodesc/proddesc_81463.htm.] Isachsen, Y.W., and Fisher, D.W., 1970, Geologic map of New York—Adirondack sheet: New York State Museum, Map and Chart Series 15, 1 sheet, scale 1:250,000. [Also available at ://www.nysm.nysed.gov/staffpublications/geologic-map-new-york-adirondack-sheet-1250000.] Kemp, J.F., 1898, Geology of the Lake Placid region: Bulletin of the New York State Museum, v. 5, no. 21, p. 51–65. Lupulescu, M.V., Chiarenzelli, J.R., Pullen, A.T., and Price, J.D., 2011, Using pegmatite geochronology to constrain temporal events in the Adirondack Mountains: Geosphere, v. 7, no. 1, p. 23–39, accessed May 7, 2025, at ://doi.org/10.1130/GES00596.1. Lupulescu, M.V., Chiarenzelli, J.R., and Bailey, D.G., 2012, Mineralogy, classification, and tectonic setting of the granitic pegmatites of New York State, USA: The Canadian Mineralogist, v. 50, no. 6, p. 1713–1728, accessed May 7, 2025, at ://doi.org/10.3749/canmin.50.6.1713. McLelland, J., Chiarenzelli, J., Whitney, P., and Isachsen, Y., 1988, U-Pb zircon geochronology of the Adirondack Mountains and implications for their geologic evolution: Geology, v. 16, no. 10, p. 920–924, accessed April 14, 2021, at ://doi.org/10.1130/0091-7613(1988)016<0920:UPZGOT>2.3.CO;2. McLelland, J.M., Bickford, M., Hill, B.M., Clechenko, C.C., Valley, J.W., and Hamilton, M.A., 2004, Direct dating of Adirondack massif anorthosite by U-Pb SHRIMP analysis of igneous zircon—Implications for AMCG complexes: Geological Society of America Bulletin, v. 116, nos. 11–12, p. 1299–1317. [Also available at ://doi.org/10.1130/B25482.1.] Miller, W.J., 1918, Adirondack anorthosite: Bulletin of the Geological Society of America, v. 29, no. 1, p. 399–462. [Also available at ://doi.org/10.1130/ GSAB-29-399.] Miller, W.J., 1919, Magnetic iron ores of the Clinton County, New York: Economic Geology, v. 14, no. 7, p. 509–535. [Also available at ://doi.org/10.2113/ gsecongeo.14.7.509.] Postel, A.W., 1952, Geology of the Clinton County magnetite district: U.S. Geological Survey Professional Paper 237, 88 p., 3 pls. [Also available at ://doi.org/ 10.3133/pp237.] Regan, S.P., Chiarenzelli, J.R., McLelland, J.M., and Cousens, B.L., 2011, Evidence for an enriched asthenospheric source for coronitic metagabbros in the Adirondack Highlands: Geosphere, v. 7, no. 3, p. 694–709. [Also available at ://doi.org/10.1130/GES00629.1.] Regan, S.P., Walsh, G.J., Williams, M.L., Chiarenzelli, J.R., Toft, M., and McAleer, R., 2019, Syn-collisional exhumation of hot middle crust in the Adirondack Mountains (New York, USA)—Implications for extensional orogenesis in the southern Grenville Province: Geosphere, v. 15, no. 4, p. 1240–1261, accessed May 7, 2025, at ://doi.org/10.1130/GES02029.1. Rickard, L.V., Isachsen, Y.W., and Fisher, D.W., 1970, Geologic map of New York: New York State Museum, Map and Chart Series 15, 6 sheets, scale 1:250,000. [Also available at ://.usgs.gov/Prodesc/proddesc_98670.htm.] Rowley, E.B., 1962a, Rare-earth pegmatite discovered in Adirondack Mountain area, Essex County, New York: Rocks & Minerals, v. 37, nos. 7–8, p. 341–347, accessed May 7, 2025, at ://doi.org/10.1080/00357529.1962.11766273. Rowley, E.B., 1962b, Rare-earth pegmatite discovered in Adirondack Mountain area, Essex County, New York, Part II: Rocks & Minerals, v. 37, nos. 9–10, p. 453–460, accessed May 7, 2025, at ://doi.org/10.1080/ 00357529.1962.11766306. Streckeisen, A., 1976, To each plutonic rock its proper name: Earth-Science Reviews, v. 12, no. 1, p. 1–33, accessed July 7, 2023, at ://doi.org/ 10.1016/0012-8252(76)90052-0. Tan, L.-P., 1966, Major pegmatite deposits of New York State: New York State Museum and Science Service Bulletin, no. 408, 138 p. Valley, P.M., Fisher, C.M., Hanchar, J.M., Lam, R., and Tubrett, M., 2010, Hafnium isotopes in zircon—A tracer of fluid-rock interaction during magnetite-apatite (“Kiruna-type”) mineralization: Chemical Geology, v. 275, nos. 3–4, p. 208–220, accessed May 7, 2025, at ://doi.org/10.1016/ j.chemgeo.2010.05.011. Valley, P.M., Hanchar, J.M., and Whitehouse, M.J., 2009, Direct dating of Fe oxide- (Cu-Au) mineralization by U/Pb zircon geochronology: Geology, v. 37, no. 3, p. 223–226, accessed May 7, 2025, at ://doi.org/10.1130/G25439A.1. Valley, P.M., Hanchar, J.M., and Whitehouse, M.J., 2011, New insights on the evolution of the Lyon Mountain Granite and associated Kiruna-type magnetite-apatite deposits, Adirondack Mountains, New York State: Geosphere, v. 7, no. 2, p. 357–389, accessed May 7, 2025, at ://doi.org/ 10.1130/GES00624.1. Valley, P.M., Parker, M., Walsh, G.J., Orndorff, R.C., Walton, M.S., Jr., and Crider, E.A., Jr., 2026, Database for the preliminary bedrock geologic map of the Port Henry quadrangle, Essex County, New York, and Addison County, Vermont: U.S. Geological Survey data release, ://doi.org/10.5066/ P13HYFPM. Walsh, G.J., Orndorff, R.C., and McAleer, R.J., 2022, Bedrock geologic map of the Crown Point quadrangle, Essex County, New York, and Addison County, Vermont: U.S. Geological Survey Scientific Investigations Map 3491, 1 sheet, scale 1:24,000, 44-p. pamphlet, accessed May 7, 2025, at ://doi.org/ 10.3133/sim3491. Walton, M., 1966, Explanation for bedrock maps of the Paradox Lake, Elizabethtown, Port Henry and Ticonderoga 15′ quadrangles, and contained 7-1/2′ quadrangles: New York State Geological Survey, Open-File Report 1m4628, unpublished archive manuscript text, 47 p. Welby, C.W., 1961, Bedrock geologic map of the central Champlain Valley of Vermont: Vermont Geological Survey Bulletin 14, 296 p., 3 pls., scale 1:62,500. [Also available at ://dec.vermont.gov/sites/dec/files/geo/ bulletins/Welby_1961sm.pdf.] unit is well exposed on the western shore of Lake Champlain in the village of Port Henry, Mullen Bay, and along Mullen Brook. Thickness is extremely variable (based on the paleotopographic surface) and is as much as 200 ft (61 m) PROTEROZOIC IGNEOUS AND METAMORPHIC ROCKS NEOPROTEROZOIC IGNEOUS ROCKS Mafic dikes (Ediacaran)—Dark-gray to olive-green or black, black to dark-reddish-green or rusty maroon weathering, aphanitic to phaneritic, equigranular diabase dikes. Dikes may show chilled margins, and thicker dikes are medium- to coarse-grained in the center and consist mostly of clinopyroxene and plagioclase exhibiting an ophitic texture, with minor amounts of olivine altered to serpentine, chlorite, biotite, opaques, and uralite alteration. Measured dikes range in thickness from 0.01 to 2 meters (m). The steeply dipping dikes trend northeast with a mean strike and dip of 051°/80°. Mafic dikes crosscut every Proterozoic rock unit, but are not found in the Paleozoic rocks, and thus predate the basal unconformity. Measured dikes are shown with strike-and-dip symbols. Dikes are locally coincident with brittle faults MESOPROTEROZOIC IGNEOUS ROCKS Late- to Post-Tectonic Igneous Rocks Pegmatite dikes (Mesoproterozoic)—Pink and white to white, coarse- to very coarse-grained, hornblende-biotite granite pegmatite and clinopyroxene granite pegmatite that occurs as undeformed or weakly deformed dikes and sills. Magnetite is common. In the adjacent Witherbee quadrangle, some pegmatite bodies were mined for magnetite. Locally, the unit contains garnet and graphite. Rose quartz was observed in granite pegmatite intruding unit Ym near the contact with units Yhg and Ylg. May contain epidote, allanite-Ce, polycrase-Y, titanite, zircon, and fluorite; the feldspars are mostly microcline and albite (Lupulescu and others, 2011). Some dikes are slightly to moderately radioactive. The highest gamma-ray measurement was 31 times background or 310 microroentgens per hour (uR/hr). This pegmatite is near the north end of the Cheever pits and has been quarried or prospected. The pegmatites are reportedly low in lithium but elevated in rare earth elements (Rowley, 1962a, b; Tan, 1966; Lupulescu and others, 2012) Syn- to Post-Tectonic Igneous Rocks Lyon Mountain Granite Gneiss (Postel, 1952) Leucogranite gneiss (Mesoproterozoic)—Pink to white, light-gray to white and locally rusty-tan weathering, fine- to medium-grained, equigranular, variably well layered and gneissic to poorly foliated, undifferentiated quartz-plagioclase-alkali feldspar rocks consisting of microperthite granite, microcline granite, quartz syenite, alkali feldspar granite (alaskite), syenogranite, monzogranite, and quartz-albite rock (metasomatic trondhjemite or albitite). Contains ubiquitous, as much as 5 percent magnetite, and trace amounts to 5 percent biotite, hornblende, or clinopyroxene; mafic minerals are either disseminated or occur in thin bands defining a foliation or lamination. Perthitic feldspar may exhibit rims of plagioclase. The amounts of biotite, hornblende, and clinopyroxene vary and most samples are dominated by only one of the minerals. In many places, magnetite is the only mafic mineral visible in hand sample. Clinopyroxene, where present, is typically aegirine (Valley and others, 2011). The granite locally contains accessory garnet, chlorite, titanite, titanomagnetite, fluorapatite, and trace amounts of zircon, monazite, and allanite. Garnet is locally abundant, especially near contacts with Ybg and Yhg granitic gneiss. Where the unit has been altered by sodium metasomatism, arfvedsonite, hedenbergite, and andradite garnet may be locally present (Valley and others, 2009, 2011). Rare magnetite-quartz-sillimanite nodules are present on the east side of Coot Hill and at the contact between Ylg and Ybg, immediately east of the rail line on the shore of Lake Champlain, south of Port Henry Village. The unit is the host to the majority of magnetite ore deposits in the Port Henry quadrangle and the eastern Adirondacks. Layer-parallel and less abundant crosscutting veins of magnetite and quartz occur locally. The unit contains both layer-parallel crosscutting magnetite-bearing clinopyroxene or biotite granitic pegmatite. The unit is well exposed and commonly forms resistant, glacially rounded blocky outcrops. The leucogranite is well layered at the centimeter (cm)- to m-scale and varies in modal grain size and primary mafic mineralogy between individual, submeter thick layers, but it is generally homogenous at the map scale; no systematic variation could be mapped. The unit locally contains partially assimilated xenoliths and screens of amphibolite (Ya); xenoliths and screens of migmatitic paragneiss, quartzite, and metagabbro are less common. Contacts between unit Ylg and adjacent paragneiss Ybg are gradational and marked by a transitional zone of migmatite in both rocks, and a change from microperthite granite to two feldspar granite. In the Port Henry quadrangle, Ylg was frequently mapped separating Yhg from Yanw and Ym from Ygb. The Lyon Mountain Granite Gneiss intrudes Ygb and Yanw over a 5–30 m zone as layer parallel dikes and sheets. The thickness and number of dikes increases as the contact is approached and vary from cm- to m-scale. Adjacent to regions of magnetite ore there is evidence for metasomatic alteration by potassic and sodic fluids (Valley and others, 2009, 2010, 2011), and the granite near ore deposits is commonly bleached white and consists of a magnetite-quartz-albite assemblage. These sodium-altered halos are gradational. Distal to the ore bodies, hydrothermal albite forms rims on grains of microperthite. At the margin of the ore bodies, albite replacement of microperthite reaches 100 percent. At the Cheever mine, the sodic alteration zone is approximately 30–50 m wide above the ore body. Chemically, the rocks plot as A-type quartz alkali-feldspar syenite, and alkali feldspar granite. The unit forms the footwall of the Great Unconformity exposed immediately west of route 9 at the southern edge of town Syn- to Pre-Tectonic Igneous Rocks Pyroxene-hornblende granitic gneiss (Mesoproterozoic)—Cinnamon brown to tan, gray to olive-gray, and white weathering, medium- to coarse-grained, largely equigranular, moderately to strongly foliated pyroxene-hornblende granitoid gneiss ranging in composition from granite to granodiorite, charnockite, mangerite, monzonite, quartz monzonite, and syenite. Contains primary plagioclase and ilmenite, with variable amounts of microperthite, quartz, clinopyroxene, orthopyroxene, and accessory magnetite, zircon, and orthopyroxene. Orthopyroxene is not present in all samples, and the rock in many places is largely a hornblende- or clinopyroxene-bearing granitoid gneiss. Contains varying amounts of relict orthopyroxene, and pigeonite exsolution lamellae in augite, but the percentage of orthopyroxene is generally low except near the contact with Ygb. When orthopyroxene is present, it is commonly rimmed by hornblende. Hornblende, garnet, and biotite are common metamorphic phases. Regionally, the rock is part of the anorthosite-mangerite-charnockite-granite (AMCG) suite (McLelland and others, 2004; Walsh and others, 2022). In this map, the Yhg unit post-dates the leucogabbro (Yanw) and contains blocks or xenoliths of leucogabbro and anorthosite. Crosscutting relationships between Yhg and the coronitic gabbro (Ygb) are ambiguous. Field relationships suggest that Yhg is similar in age or slightly younger than Ygb. The contact between these two units is marked by a gradational transition zone 50–100 m wide. Hornblende granite gneiss becomes more syenitic or monzonitic and the percentage of orthopyroxene and clinopyroxene increases and quartz decreases to the point that its composition is gabbroic. The percentage of magnetite increases in the transition zone and layers of magnetite and clinopyroxene are present locally. Walton described this transition zone as anorthositic-charnockite (Walton, 1966). At the contact, monzonite/syenite is complexly interlayered with coronitic metagabbro. Rocks in the transition zone may be intensely sheared, moderately deformed, or retain magmatic flow textures that are completely undeformed. The variations in rock types of this unit are complexly interlayered and look similar in outcrop. For these reasons, they are shown as an undifferentiated map unit at the scale of this map. Here, we follow the suggestion of Frost and Frost (2008) and drop the many terms designated to describe various orthopyroxene- U D Ogf Oo Ov Ocp Opi Ocu O w Yhg Yanw Ygb Zd Zd Yp Yp Yp Ylg Ym Ysi Ya Yqt Ywg Ybg Ycs Qal Osp pt ti sz wt Yggn Qal Mafic dikes Pegmatite dikes Trachyte dike PALEOZOIC SEDIMENTARY ROCKS PROTEROZOIC IGNEOUS AND METAMORPHIC ROCKS NEOPROTEROZOIC IGNEOUS ROCKS ORDOVICIAN Upper Ordovician Middle Ordovician MESOPROTEROZOIC PALEOZOIC NEOPROTEROZOIC Ediacaran Silicified zone QUATERNARY CAMBRIAN MESOZOIC CENOZOIC Upper Cambrian Upper and Middle(?) Cambrian Grenville Complex Syn- to Post-Tectonic Igneous Rocks Syn- to Pre-Tectonic Rocks Late- to Post-Tectonic Igneous Rocks wt Oo Unconformity Ov Unconformity Ocp Knox Unconformity Great Unconformity Osp MESOPROTEROZOIC IGNEOUS ROCKS Ylg Ya Ogf Ocu O w ti pt Yqt Ywg Ym Ycs Ybg Ysi Ya Yhg Ygb Yanw Yggn Opi HOLOCENE DEPOSITS QUATERNARY DEPOSITS CORRELATION OF MAP UNITS Lower Ordovician Paleozoic Cleavage Brittle Faulting RELATIVE TIMING OF DEFORMATION EVENTS Penetrative Deformation D2 Cryptic Deformation D1 Boudinage and Shear Bands D4 Doming D3 Rifting MESOPROTEROZOIC METASEDIMENTARY AND METAIGNEOUS ROCKS Lyon Mountain Granite Gneiss (Postel, 1952) Unconformity Stratigraphic order is unknown. Units are listed from top to bottom as the map pattern dictates. MESOZOIC FAULT ROCKS MESOZOIC IGNEOUS ROCKS sz Yp Yp Yp Zd Zd Geology mapped by Walton (1950–1960), Orndorff (2019–2020), Walsh (2019–2020), Valley (2019–2022), and Parker (2020–2022) Compilation by Valley and Crider Edited by David A. Shields MAP LOCATION NEW YORK Vt. 1 MILE CONTOUR INTERVAL 5 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929 7000 FEET 1 KILOMETER SCALE 1:24 000 1/2 APPROXIMATE MEAN DECLINATION, 2026 TRUE NORTH 13 / ° MAGNETIC NORTH Base modified from New York State Department of Transportation, Port Henry, 1969 Universal Transverse Mercator Projection, zone 18 1000-meter Universal Transverse Mercator grid ticks, zone 18 North American Datum of 1983 ? ? ? ? ? D U U D D U ? ? ? ? U D D U U D U D U D U D U D U D U D U D U D U D U D U D D U D U D U U D U D U D U D U D U D U D U D U D U D U D U D U D U D U D U D U D ? VINEY ARD RO AD FAUL T VINEY AR D R OA D FAULT VIN EY ARD RO AD FA ULT LAKE CHAMPLAIN FAULT H ENE Y
M OU N T AI N SHEA R ZON E U D U D AD R ONDA CK P A R K FAUL T ADIRO NDACK PA RK FAULT Yhg Ocp Opi Ogf Ocu Ocu Ya Ybg Ya Ybg Ylg Ylg Yhg Ylg Ylg Ya Ylg Ybg Ylg Ya Ya pt wt Ybg Ocp Ocp Ocp sz Ov Ov sz sz Oo Oo Oo Yggn sz Ogf Qal Ycs Ylg Ylg Ym Ym Ya Ysi Ycs Osp Osp Ylg Ylg Ym pt pt Ysi Ysi ti Ya Ym Ym Yggn Ysi Ycs Ycs Ycs Ycs Ya Ya Ya Yqt Yqt Ylg Ya Ycs wt Yqt O w Ylg Ygb Ylg Ywg Ym Ysi Yqt wt Ya Ym Yggn Ysi Yhg Yhg Opi Opi Opi Ywg Ycs Ya Ysi Ysi Ysi Yanw Yanw Yhg Yhg Ya Ya Yqt Ya Ya Ylg Ylg Ylg Ylg Ylg Ylg Ylg Ylg Ycs Ygb Ya Ylg Ocp Ya Yhg Yanw Yanw Yhg Ycs Ysi Yhg Ylg Qal Ov Ym Ysi Ylg Ym Ym Ym Ym Ym Ycs Ylg Yhg Ygb Ygb Ygb Yhg Ym Yanw Yhg Oo Ylg Ylg Yhg Yhg Yhg Yhg Yhg Ya Ygb Ygb Ygb Ygb Ym Yhg Yhg Yanw Yanw Yhg Yhg Ygb Ygb Ylg Ygb Ylg Ylg Ylg Ogf Ogf Ylg Yhg Yanw Ybg Yhg Ygb Yhg Yhg Ygb Ygb Yanw Ylg pt pt (concealed) Yhg Opi Yhg Ylg Yanw Yanw Yanw Yhg Yanw Yanw Osp Ogf Oo Ov Ocp Osp Osp Ocp Osp Ov Ocp Opi Lee Mine Mineville Mine Essex Mining Company Mine Butler Mine Craig Harbor Mine Goff Mine Pilfershire Mine Cheever Mine 4886000mN 4874000mN 621000mE 630000mE 73°30’ 44°07’30” 73°22’30” 44°07’30” 44°05’ 44°02’30” 44°05’ 44°02’30” 73°30’ 44°00’ 73°22’30” 44°00’ 73°27’30” 73°25’ 73°27’30” 73°25’ U.S. Department of the Interior U.S. Geological Survey Open-File Report 2026–1062 Prepared in cooperation with the State of Vermont, Vermont Agency of Natural Resources, Vermont Geological Survey and the State of New York, Department of Education, New York Geological Survey