| 2.1 Has required elements: nonspatial tables DataSources, DescriptionOfMapUnits, GeoMaterialDict; feature dataset GeologicMap with feature classes ContactsAndFaults and MapUnitPolys | PASS |
| 2.2 Required fields within required elements are present and correctly defined | PASS |
| 2.3 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 2 topology rules: no internal gaps or overlaps in MapUnitPolys, boundaries of MapUnitPolys are covered by ContactsAndFaults | PASS |
| 2.4 All map units in MapUnitPolys have entries in DescriptionOfMapUnits table | PASS |
| 2.5 No duplicate MapUnit values in DescriptionOfMapUnit table | PASS |
| 2.6 Certain field values within required elements have entries in Glossary table | PASS |
| 2.7 No duplicate Term values in Glossary table | PASS |
| 2.8 All xxxSourceID values in required elements have entries in DataSources table | PASS |
| 2.9 No duplicate DataSources_ID values in DataSources table | PASS |
| 3.1 Table and field definitions beyond Level 2 conform to GeMS schema | PASS |
| 3.2 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 3 topology rules: No ContactsAndFaults overlaps, self-overlaps, or self-intersections. | PASS |
| 3.3 No missing required values | PASS |
| 3.4 No missing terms in Glossary | PASS |
| 3.5 No unnecessary terms in Glossary | PASS |
| 3.6 No missing sources in DataSources | PASS |
| 3.7 No unnecessary sources in DataSources | PASS |
| 3.8 No map units without entries in DescriptionOfMapUnits | PASS |
| 3.9 No unnecessary map units in DescriptionOfMapUnits | PASS |
| 3.10 HierarchyKey values in DescriptionOfMapUnits are unique and well formed | PASS |
| 3.11 All values of GeoMaterial are defined in GeoMaterialDict. GeoMaterialDict is as specified in the GeMS standard | PASS |
| 3.12 No duplicate _ID values | PASS |
| 3.13 No zero-length, whitespace-only, or bad null values | PASS |
| MapUnit | DescriptionOfMapUnits | GeologicMap |
|---|---|---|
| Pc | X | X |
| Qt | X | X |
| Pp | X | X |
| Mg | X | X |
| Pa | X | X |
| Dnm | X | X |
| Do | X | X |
| DSkh | X | X |
| St | X | X |
| Qcl | X | X |
| Df | X | X |
| PPd | X | X |
| Qps | X | X |
| Qal | X | X |
| Sto | X | X |
| Oj | X | X |
| Pm | X | X |
| Dm | X | X |
| Smb | X | X |
| Dh | X | X |
| Dhbs | X | X |
| Swc | X | X |
| Qdf | X | X |
| Srk | X | X |
| MDr | X | X |
| Mp | X | X |
| Mmc | X | X |
| OBJECTID | Source | Notes | URL | DataSources_ID |
|---|---|---|---|---|
| 20 | Neuendorf et al., eds., 2011 | modified from Neuendorf, K.K.E., Mehl Jr., J.P., and Jackson, J.A., eds. 2011. Glossary of Geology (Fifth Edition, Revised). Alexandria, VA. American Geological Institute. 783 p. | https://www.americangeosciences.org/pubs/glossary | AGI_2011 |
| 8 | FGDC, 2006 | Federal Geographic Data Committee [prepared for the Federal Geographic Data Committee by the U.S. Geological Survey], 2006, FGDC Digital Cartographic Standard for Geologic Map Symbolization: Reston, Va., Federal Geographic Data Committee Document Number FGDC-STD-013-2006, 290 p., 2 plates. | https://ngmdb.usgs.gov/fgdc_gds/geolsymstd.php | FGDC-STD-013-2006 |
| 7 | definitions copied from GeMS, 2020 | U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org//10.3133/tm11B10. | https://pubs.usgs.gov/publication/tm11B10 | GeMS_2020 |
| 23 | MD iMAP, State Boundary | Maryland State, MD iMAP Data Catalog (DoIT), Maryland Political Boundaries - County Boundary, publ. 2015-07, updated 2025-05-12, accessed 2025-11. | https://mdgeodata.md.gov/imap/rest/services/Boundaries/MD_PoliticalBoundaries/FeatureServer/1 | IMAP_PolB_CB_2015 |
| 3 | Brezinski, 2019 | Brezinski, D.K., 2019. Geologic Map of the Accident and McHenry Quadrangles, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, ACCID_McHEN2019.1.0, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_ACCID_McHEN2019.1.0 |
| 26 | Glaser, 1994a | Glaser, J.D., 1994a. Geologic Map of the Artemas quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, 2012. | http://www.mgs.md.gov/publications/maps.html | MGS_ARTEM1994.1 |
| 19 | Brezinski, 1988 | Brezinski, D.K., 1988. Geologic Map of the Avilton and Frostburg Quadrangles, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_AVILT_FROST1988 |
| 17 | Brezinski, in prep (2027) | Brezinski, D.K., 2027 (in prep). Geologic Map of the Maryland Portion of the Barton and Westernport Quadrangles, Garrett and Allegany Counties, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, BARTO_WESTE2027.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_BARTO_WESTE2027.1 |
| 27 | Glaser, 1994b | Glaser, J.D., 1994b. Geologic Map of the Bellegrove quadrangle, Allegany and Washington Counties, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, 2012. | http://www.mgs.md.gov/publications/maps.html | MGS_BELLE1994.1 |
| 14 | Brezinski, in prep (2026b) | Brezinski, D.K., 2026b (in prep). Geologic Map of the Bittinger Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, BITTI2026.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_BITTI2026.1 |
| 28 | Glaser, 1994c | Glaser, J.D., 1994c. Geologic Map of the Cresaptown quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, R. Kavage Adams, and W.K. Vincett, III, 2024. | http://www.mgs.md.gov/publications/maps.html | MGS_CRESA1994.1 |
| 25 | Glaser and Brezinski, 1994 | Glaser, J.D., and Brezinski, D.K., 1994. Geologic Map of the Cumberland quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Modified by D.K. Brezinski, 2012. Field checked and modified by W.K. Vincett, III, 2024. | http://www.mgs.md.gov/publications/maps.html | MGS_CUMBE1994.1 |
| 16 | Brezinski, in prep (2026d) | Brezinski, D.K., 2026d (in prep). Geologic Map of the Deer Park Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, DEERP2026.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_DEERP2026.1 |
| 33 | Brezinski, D.K., field observations | field data collection and interpretations by David Brezinski of the Maryland Geological Survey | None | MGS_DKB |
| 29 | Glaser, 1994d | Glaser, J.D., 1994d. Geologic Map of the Flintstone quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, 2012. | http://www.mgs.md.gov/publications/maps.html | MGS_FLINT1994.1 |
| 4 | Kavage Adams and Brezinski, 2025 | Kavage Adams, R., and Brezinski, D.K., 2025. Geologic Map of the Maryland Portion of the Friendsville Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, FRIEN2025.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_FRIEN2025.1 |
| 1 | Brezinski et al., 2025 | Brezinski, D.K., Vincett, W.K., III, and Kavage Adams, R., 2025. Bedrock and Surficial Geologic Map of Garrett and Allegany Counties, Maryland. Maryland Geological Survey, County Geologic Map, GAAL2025.1.1, scale 1:100,000. | http://www.mgs.md.gov/publications/maps.html | MGS_GAAL2025.1.1 |
| 15 | Brezinski, in prep (2026c) | Brezinski, D.K., 2026c (in prep). Geologic Map of the Maryland Portions of the Gorman and Mount Storm Quadrangles, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, GORMA_MOUNS2026.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_GORMA_MOUNS2026.1 |
| 24 | Brezinski, in prep (2026e) | Brezinski, D.K., 2026e (in prep). Geologic Map of the Maryland Portion of the Grantsville Quadrangle, Garrett County, Maryland, Maryland Geological Survey, Open-File Geologic Map, GRANT2026.OF, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_GRANT2026.OF |
| 32 | Glaser, J.D., field observations | field data collection and interpretations by John Glaser of the Maryland Geological Survey | None | MGS_JDG |
| 13 | Brezinski, in prep (2026a) | Brezinski, D.K., 2026a (in prep). Geologic Map of the Maryland Portion of the Kitzmiller Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, KITZM2026.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_KITZM2026.1 |
| 21 | Glaser and Brezinski, 1998 | Glaser, J.D., and Brezinski, D.K., 1998. Geologic Map of the Lonaconing quadrangle, Allegany and Garrett Counties, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by W.K. Vincett, III, 2024. | http://www.mgs.md.gov/publications/maps.html | MGS_LONAC1998.1 |
| 6 | Brezinski and Kavage Adams, 2025 | Brezinski, D.K., and Kavage Adams, R., 2025. Geologic Map of the Maryland Portion of the Oakland Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, OAKLA2025.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_OAKLA2025.1 |
| 30 | Glaser, 1994e | Glaser, J.D., 1994e. Geologic Map of the Oldtown quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, 2012. | http://www.mgs.md.gov/publications/maps.html | MGS_OLDTO1994.1 |
| 31 | Glaser, 1994f | Glaser, J.D., 1994f. Geologic Map of the Paw Paw quadrangle, Allegany County, Maryland. Maryland Geological Survey, Open-File Geologic Map, scale 1:24,000. Field checked and modified by D.K. Brezinski, 1999. | http://www.mgs.md.gov/publications/maps.html | MGS_PAWPA1994.1 |
| 37 | Brezinski et al., 2023 | Brezinski, D.K., Kavage Adams, R., and Sylvia E.R., 2023. Allegany County Highway Rock Cut Inventory and Slope Failure Potential: Maryland Geological Survey, Report of Investigations 89, 50 p. | http://www.mgs.md.gov/publications/report_pages/RI_89.html | MGS_RI_89 |
| 34 | Kavage Adams, R., field observations | field data collection and interpretations by Rebecca Kavage Adams of the Maryland Geological Survey | None | MGS_RKA |
| 5 | Kavage Adams, 2025 | Kavage Adams, R., 2025. Geologic Map of the Maryland Portion of the Sang Run Quadrangle, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, SANGR2025.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_SANGR2025.1 |
| 18 | Brezinski and Glaser, 2003 | Brezinski, D.K., and Glaser, J.D., 2003. Geologic Map of the Maryland Portions of the Table Rock and Davis Quadrangles, Garrett County, Maryland. Maryland Geological Survey, Quadrangle Geologic Map, TBLDV2003.1, scale 1:24,000. | http://www.mgs.md.gov/publications/maps.html | MGS_TBLDV2003.1 |
| 35 | Vincett, W.K., III, field observations | field data collection and interpretations by William Vincett of the Maryland Geological Survey | None | MGS_WKV |
| 2 | Brezinski and Conkwright, 2013 | Brezinski, D.K., and Conkwright, R.D., 2013. Geologic Map of Garrett, Allegany, and western Washington Counties, Maryland. Maryland Geological Survey, Regional Geologic Map, WMD2013.1.2, scale 1:100,000. | http://www.mgs.md.gov/publications/maps.html | MGS_WMD2013.1.2 |
| 9 | National Hydrography Dataset | U.S. Geological Survey, 2023, National Hydrography Dataset (NHD) - USGS National Map Downloadable Data Collection: USGS - National Geospatial Technical Operations Center (NGTOC). | https://www.sciencebase.gov/catalog/item/4f5545cce4b018de15819ca9 | NHD_2023 |
| 36 | Schaney et al., (in prep) | Schaney, M.L., Coughenour, C., Schaney, C., and Kavage Adams, R., (in prep, expected 2026). Investigating The Glades: Pedology, Paleoclimatology, and Carbon Storage. (Manuscript in preparation). | None | Schaney_2026 |
| 12 | Southworth et al., 2001 | Southworth, S., Brezinski, D.K., Orndorff, R.C., Chirico, P.G., and Lagueux, K., 2001. Digital Geologic Map and Database of the Chesapeake and Ohio Canal National Historical Park, District of Columbia, Virginia, Maryland, and West Virginia. U.S. Geological Survey Open File Report 01-188. | https://pubs.usgs.gov/of/2001/of01-188/ | USGS_OFR_01-188 |
| OBJECTID | MapUnit | Name | FullName | Age | Description | HierarchyKey | ParagraphStyle | Label | Symbol | AreaFillRGB | AreaFillPatternDescription | DescriptionSourceID | GeoMaterial | GeoMaterialConfidence | DescriptionOfMapUnits_ID |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | None | SURFICIAL UNITS | SURFICIAL UNITS | None | None | 01 | DMU-Heading1 | None | None | None | None | None | None | None | DMU_01 |
| 2 | Qal | Alluvium | Alluvium | Quaternary | Unconsolidated reddish brown to tan, sand, silt, pebbles and cobbles that commonly weather to yellow, orange, and orange-brown. Mapped alluvium deposits include those formed along modern and ancient streams, and marsh deposits formed over older bog deposits. | 01-01 | DMU Unit 1 | Qal | 40 | 255,255,179 | None | MGS_GAAL2025.1.1 | Alluvial sediment | High | DMU_02 |
| 3 | Qps | Peatland/Swamp deposits | Peatland/Swamp deposits | Quaternary | Unconsolidated dark gray to black, organic-rich soil to peat. These materials accumulated in poorly drained areas typically underlain by the Greenbrier Formation and are likely remnants of late Pleistocene to Holocene glades and lakes. These sediments are water-logged during parts of the year and are poor agricultural lands. Radiocarbon (Carbon-14) dates from peat deposits in the Glades peatland in Garrett County are between 25-10 kya (Schaney et al., in prep). Thickness is typically less than 3 feet, but may exceed 10 feet (1-3 m). | 01-02 | DMU Unit 1 | Qps | 120 | 235,255,222 | None | MGS_GAAL2025.1.1|Schaney_2026 | Peat and muck | Medium | DMU_03 |
| 4 | Qcl | Colluvium/Landslide deposits, undivided | Colluvium/Landslide deposits, undivided | Quaternary | Unsorted mass of boulders and cobbles that form on steep slopes overlying and downslope from sandstone units. These deposits are largely the result of frost wedging and slow mass wasting and movement. Topographically, these accumulations exhibit an irregular upper surface, tend to thicken downslope, and rarely have soil cover. Thickness ranges from less than 3 feet to 50 feet (1-15 m). Areas identified as landslides consist of coherent masses of bedrock that have been detached up slope, and have moved rapidly downhill under the influence of gravity. Many of these features are mapped on LiDAR hillshade digital elevation models. Because some of these deposits intergrade they are mapped together. | 01-03 | DMU Unit 1 | Qcl | 62 | 255,222,128 | None | MGS_GAAL2025.1.1 | Colluvium and other widespread mass-movement sediment | High | DMU_04 |
| 5 | Qt | Terrace deposits | Terrace deposits | Quaternary | Reddish sandy soil containing cobbles and boulders. Clasts are typically tan-weathering, well-rounded, and preserved on low-relief areas elevated above the current river systems. | 01-04 | DMU Unit 1 | Qt | 71 | 255,235,102 | None | MGS_GAAL2025.1.1 | Alluvial sediment | High | DMU_05 |
| 6 | Qdf | Debris Flow deposits | Debris Flow deposits | Quaternary | Poorly sorted to unsorted deposit of cobbles, sand, and mud formed on steep slopes along the eastern slope of Dans Mountain in Allegany County. These deposits are interpreted as resulting from rapid mass wasting resulting from precipitation events. These accumulations exhibit a lobate toe and narrow upper slope with sediment size ranging from boulders and cobbles in the higher-elevation proximal region to unsorted sand and cobbles in distal portions of the flows. Similar features were recognized and mapped as slide and/or colluvium in Cresaptown and Lonaconing quadrangles (Glaser, 1994c; Glaser and Brezinski, 1998). The full thickness was not determined, but is estimated to be 3 feet (1 m) at the downslope edge of the toe to more than 50 feet (15 m). These features are mapped largely from LiDAR digital elevation models and identified in part by abundant solifluction and other slope-movement landforms. | 01-05 | DMU Unit 1 | Qdf | 73 | 255,204,102 | None | MGS_GAAL2025.1.1|MGS_LONAC1998.1|MGS_CRESA1994.1 | Debris flows, landslides, and other localized mass-movement sediment | Medium | DMU_06 |
| 7 | None | BEDROCK UNITS | BEDROCK UNITS | None | None | 02 | DMU-Heading1 | None | None | None | None | None | None | None | DMU_07 |
| 8 | PPd | Dunkard Formation | Dunkard Formation | Permian-Pennsylvanian | Interbedded, medium gray to dark gray, carbonaceous, silty shale and siltstone; light to medium gray, micaceous, medium- to coarse-grained sandstone; and thin, discontinuous nodular limestone, and thin coal beds. The Dunkard Formation caps several hills in the Georges Creek Syncline along the Garrett-Allegany County border, and may be as much as 250 feet (76 m) thick. | 02-01-01 | DMU Unit 1 | P*d | 700 | 102,255,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_08 |
| 9 | Pm | Monongahela Group | Monongahela Group | Pennsylvanian | Interbedded, medium gray to dark gray, carbonaceous, silty shale and siltstone; light to medium gray, micaceous, medium- to coarse-grained sandstone, and thin, discontinuous, nodular limestone, and coal beds. The thickness of the Monongahela Group is 225 to 250 feet (68 to 76 m). | 02-02 | DMU Unit 1 | *m | 611 | 128,235,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_09 |
| 10 | Pc | Conemaugh Group, undivided | Conemaugh Group, undivided | Pennsylvanian | Interbedded, light gray, micaceous sandstone and gray silty shale and thin, dark gray, marine shales in the lower half of the group, and greenish gray and reddish brown to variegated mudstone, shale, claystone, and nodular nonmarine limestone in its upper part. The Conemaugh Group is 800 to 900 feet thick (245-275 m). | 02-03 | DMU Unit 1 | *c | 321 | 204,235,222 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly sandstone | High | DMU_10 |
| 11 | Pa | Allegheny Formation | Allegheny Formation | Pennsylvanian | Interbedded, medium to dark gray shale and siltstone, tan to light gray sandstone, claystone, and mineable coal beds. The Allegheny Formation is between 200 to 250 feet thick (60-76 m). | 02-04-01 | DMU Unit 1 | *a | 521 | 153,235,222 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_11 |
| 12 | Pp | Pottsville Formation | Pottsville Formation | Pennsylvanian | Dominantly light gray to tan, medium- to coarse-grained sandstone and conglomerate with subordinate amounts of dark gray shale, siltstone, and coal. Total thickness for the unit is 180 to 200 feet (55-60 m). | 02-05-01 | DMU Unit 1 | *p | 733 | 102,204,204 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone | High | DMU_12 |
| 13 | Mmc | Mauch Chunk Formation | Mauch Chunk Formation | Mississippian | Interbedded, reddish brown shale; variegated, root-mottled mudstone and siltstone, and reddish brown to greenish gray lenticular sandstone. The Mauch Chunk Formation is approximately 600 feet (180 m) thick in Allegany County and thins westward to 300 feet (90 m) in thickness in western Garrett County. | 02-06-01 | DMU Unit 1 | Mmc | 603 | 128,204,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_13 |
| 14 | Mg | Greenbrier Formation | Greenbrier Formation | Mississippian | Light gray, cross-bedded, sandy limestone to calcareous sandstone at the base (Loyalhanna Member); overlain by interbedded, reddish, fossiliferous mudstone, and tan to reddish brown, fine-grained sandstone, and reddish brown siltstone and variegated shale (Savage Dam Member); succeeded by thin- to medium-bedded, light to medium gray, argillaceous, fossiliferous limestone at the top (Wymps Gap Member). The Greenbrier Formation is 150 to 200 feet thick (45-60 m). | 02-07-01 | DMU Unit 1 | Mg | 501 | 153,235,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly carbonate rock | High | DMU_14 |
| 15 | Mp | Purslane Formation | Purslane Formation | Mississippian | Light gray, tan, and reddish brown, coarse-grained to conglomeratic, thick-bedded to cross-bedded sandstone, thin beds of gray shale, and coaly shale. The Purslane Formation is more than 300 feet (90 m) thick in western Washington County and thins westward to approximately 150 feet (45 m) thick in western Garrett County. | 02-08-01 | DMU Unit 1 | Mp | 301 | 204,235,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly sandstone | High | DMU_15 |
| 16 | MDr | Rockwell Formation | Rockwell Formation | Mississippian-Devonian | Interbedded, gray, silty shale, light gray to tan sandstone, and coaly and reddish shale. In Allegany and Washington counties, a reddish brown to gray, polymictic diamictite marks the base of the formation. The Rockwell Formation is more than 400 feet (120 m) thick in eastern Allegany County; thins to less than 100 feet (30 m) in southern Garrett County. | 02-09-01 | DMU Unit 1 | MDr | 614 | 128,179,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_16 |
| 17 | Dh | Hampshire Formation | Hampshire Formation | Devonian | Interbedded, reddish brown to brownish red, locally greenish gray sandstone, reddish brown siltstone, shale, and rooted claystone. The thickness of the Hampshire Formation varies from approximately 2,000 feet (600 m) in Garrett County to more than 3,000 feet (900 m) in eastern Allegany and western Washington counties. | 02-10-01 | DMU Unit 1 | Dh | 414 | 179,179,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_17 |
| 18 | Df | Foreknobs Formation | Foreknobs Formation | Devonian | Interbedded, olive gray medium- to coarse-grained, cross-bedded sandstone; greenish gray to dusky red, fossiliferous shale and siltstone. Thick, greater than 30 feet (10 m) sandstone intervals occur both near the base and near the top of the formation. The Foreknobs Formation ranges from 1,200 feet (365 m) thick in Garrett County to more than 1,500 feet (460 m) in thickness in eastern Allegany County. | 02-11-01 | DMU Unit 1 | Df | 303 | 204,204,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly sandstone | High | DMU_18 |
| 19 | Dhbs | Harrell Shale-Brallier-Scherr Formations, undivided | Harrell Shale-Brallier-Scherr Formations, undivided | Devonian | The Harrell Shale is a dark gray, fissile, calcareous, thinly laminated, shale that weathers to thin yellowish gray shale chips. The base of the Harrell Shale is marked by the black, very fissile Burket Shale Member. The Harrell grades eastward into the Brallier Formation. The Harrell Shale is up to 150 feet thick (45 m). The Brallier Formation is a succession of thinly interbedded, gray to olive gray shale and siltstone and thin, fine-grained sandstone. The Brallier Formation is 2,000 to 2,500 feet thick (600-760 m). The Scherr Formation is an interbedded, reddish brown to grayish brown shale; thin, gray siltstone; and fine-grained, bioturbated and fossiliferous sandstone. The thickness of the Scherr Formation is approximately 1,000 feet (300 m) in Garrett County and becomes indistinct in eastern Allegany County. | 02-12 | DMU Unit 1 | Dhbs | 524 | 153,179,222 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_19 |
| 20 | Dm | Mahantango Formation | Mahantango Formation | Devonian | Medium gray to olive gray, massive siltstone to fine-grained sandstone near the base and top of the formation. Interbedded with the siltstone intervals are thinly bedded siltstone, sandstone, and silty, hackly shale. The Mahantango Formation weathers brownish gray to grayish brown. The Mahantango Formation is approximately 1,400 feet (425 m) thick in Allegany County and thins westward to less than 1,000 feet (300 m) in thickness in the subsurface of Garrett County. | 02-13-01 | DMU Unit 1 | Dm | 403 | 179,204,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_20 |
| 21 | Dnm | Needmore-Marcellus Shales, undivided | Needmore-Marcellus Shales, undivided | Devonian | The Needmore Shale is a dark brownish gray to medium dark gray, calcareous, fossiliferous shale, with thin 1 foot (30 cm) beds of dark gray, argillaceous limestone. The upper Needmore Shale consists of approximately 35 feet (10 m) of interbedded, dark gray, argillaceous limestone and black shale. This interval is correlative with the Onondaga Limestone of New York. The top of the Needmore Shale is marked by the Tioga Bentonite, a brown, tuffaceous claystone. The Needmore Shale is 150 feet thick in Allegany County (45 m). The Marcellus Shale consists of black, brittle, fissile shale in the lower 100 feet (30 m); interbedded, thinly bedded, black limestone and shale in the middle; and very dark gray, fissile shale containing thin (0.5-1 inch, 1-2 cm) siltstone beds at the top. The Marcellus Shale is more than 350 feet (105 m) thick in western Washington County and thins to approximately 150 feet (45 m) in the subsurface at Keysers Ridge in Garrett County. | 02-14 | DMU Unit 1 | Dnm | 606 | 128,128,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_21 |
| 22 | Do | Oriskany Formation | Oriskany Formation | Devonian | Interbedded, medium to dark gray, siliceous shale, with sandy and cherty limestone near the base (Shriver Shale Member); overlain by tan fine-grained, calcareous sandstone; and then by light gray, medium- to coarse-grained, thin- to thick-bedded, calcareous sandstone at the top (Ridgely Member). The Oriskany Formation thickens to the west from approximately 50 feet (15 m) thick in western Washington County to 300 feet (90 m) thick in Allegany County. | 02-15-01 | DMU Unit 1 | Do | 314 | 204,179,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_22 |
| 23 | DSkh | Keyser-Helderberg Limestones, undivided | Keyser-Helderberg Limestones, undivided | Devonian-Silurian | The Keyser Limestone consists of light gray, coarsely crystalline crinoidal limestone in the lower 50 feet (15 m), overlain by medium to dark gray, medium- to thick-bedded, nodular, fossiliferous limestone containing dark gray chert nodules. The upper Keyser Limestone is thin-bedded, cherty, fossiliferous limestone. The Keyser is up to 300 feet (90 m) thick in western Washington County and thins to approximately 200 feet (60 m) in western Allegany County. The Helderberg Limestone consists of medium gray, medium-bedded, cherty, crinoidal limestone (New Creek Member); overlain in Allegany County by a light gray, cross-bedded calcareous sandstone (Elbow Ridge Sandstone); then a medium gray fossiliferous limestone containing beds of brown-weathering chert (Corriganville Limestone); which is succeeded by interbedded, cherty, dark gray limestone and dark calcareous shale (Licking Creek Member); and topped by a thin, black, brittle shale (Mandata Shale). The Helderberg Limestone is 150 to 180 feet (30-55 m) thick in western Maryland. | 02-16 | DMU Unit 1 | DSkh | 202 | 222,222,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Carbonate rock | High | DMU_23 |
| 24 | None | Silurian Units Undivided | Silurian Units Undivided | Silurian | None | 02-17 | DMU Unit 2 | None | None | None | None | None | Sedimentary rock | High | DMU_24 |
| 27 | Sto | Tonoloway Formation | Tonoloway Formation | Silurian | Medium to light gray, fine-grained, thinly laminated, mudcracked, dolomitic limestone with thin layers of medium gray, fine-grained limestone and tan, laminated dolomite. The Tonoloway Formation is approximately 400 feet thick (120 m). | 02-17-01 | DMU Unit 1 | Sto | 304 | 204,179,255 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Carbonate rock | High | DMU_25 |
| 30 | Swc | Wills Creek Formation | Wills Creek Formation | Silurian | Interbedded, greenish gray to light gray, calcareous shale, and tan, dolomitic shale containing mud cracks, laminations, and salt and gypsum casts. The thickness of the Wills Creek Formation is approximately 400 feet (120 m). | 02-17-02 | DMU Unit 1 | Swc | 415 | 179,153,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mudstone | High | DMU_26 |
| 31 | Smb | McKenzie-Bloomsburg Formations, undivided | McKenzie-Bloomsburg Formations, undivided | Silurian | Interbedded, gray to pale greenish gray, calcareous shale and medium to dark gray, thin-bedded, fossiliferous limestone. At the base of the McKenzie Formation a greenish gray shale is equivalent to the Rochester Shale of New York. Above the McKenzie Formation is interbedded, reddish gray to brownish gray, fine-grained sandstone and reddish hackly shale and mudrock of the Bloomsburg Formation. The McKenzie Formation is up to 300 feet thick (90 m), and the Bloomsburg Formation is approximately 30 feet (10 m) thick in western Allegany County and as much as 100 feet (30 m) in the eastern part of the county. | 02-17-03 | DMU Unit 1 | Smb | 639 | 128,000,204 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_27 |
| 32 | Srk | Rose Hill Formation-Keefer Sandstone, undivided | Rose Hill Formation-Keefer Sandstone, undivided | Silurian | The Rose Hill Formation consists of pale olive gray to pale reddish gray, fissile shale. Shales are locally interbedded with tan to reddish brown, fine-grained, thin-bedded to cross-laminated, and locally ferruginous, sandstone. The overlying Keefer Sandstone is a light gray, tan-weathering, fine to medium-grained, thin- to medium-bedded, argillaceous, bioturbated sandstone that is 10 feet (3 m) thick in western Allegany County and up to 65 feet (20 m) thick in the eastern part of the county. The approximate combined thickness of the Rose Hill Formation and Keefer Sandstone is 300 feet (90 m). | 02-17-04 | DMU Unit 1 | Srk | 446 | 179,128,179 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_28 |
| 33 | St | Tuscarora Sandstone | Tuscarora Sandstone | Silurian | Light gray, fine- to medium-grained, medium-bedded, dense sandstone. Locally, sandstone layers are interbedded with thin, gray shale. The thickness of the Tuscarora Sandstone varies from less than 50 feet (15 m) in Washington County to up to 380 feet (115 m) in western Allegany County. | 02-18-01 | DMU Unit 1 | St | 113 | 235,204,235 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone | High | DMU_29 |
| 35 | Oj | Juniata Formation | Juniata Formation | Ordovician | Interbedded, reddish brown to brownish red, fine- to medium-grained, medium- to thick-bedded, cross-bedded sandstone and micaceous siltstone and silty shale. The Juniata Formation is up to 300 feet (90 m) thick in western Allegany County. | 02-19-01 | DMU Unit 1 | Oj | 227 | 222,102,222 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sandstone and mudstone | High | DMU_30 |
| 36 | None | Martinsburg-Reedsville Formations, undivided | Martinsburg-Reedsville Formations, undivided | Ordovician | The Martinsburg and Reedsville Formations are a medium to dark gray, fissile shale at the base, overlain by medium gray, silty shale and thinly interbedded medium-grained sandstone; and then by thick-bedded, medium-grained fining-upward sandstone at the top of this interval. Regional differences in nomenclature and mapping result in these formations being undivided in the map area. These formations are up to 5,000 feet thick in western Allegany County (1,500 m). | 02-20 | DMU Unit 1 | Omr | 26 | 255,128,222 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Mostly mudstone | High | DMU_31 |
| 37 | None | Older Ordovician and Cambrian strata | Older Ordovician and Cambrian strata | Ordovician-Cambrian? | None | 02-21 | DMU Unit 1 | O-_ | 65 | 255,153,128 | None | MGS_GAAL2025.1.1|MGS_WMD2013.1.2 | Sedimentary rock | High | DMU_32 |
| OBJECTID | Term | Definition | DefinitionSourceID | Glossary_ID |
|---|---|---|---|---|
| 14 | bedding | Formed, arranged, or deposited in layers or beds, or made up of or occurring in the form of beds; esp. said of a layered sedimentary rock, deposit, or formation. The term has also been applied to nonsedimentary material that exhibits depositional layering, such as the "bedded deposits" of volcanic tuff alternating with lava in the mantle of a stratovolcano. | AGI_2011 | GLO13 |
| 11 | border | Border line for state or county | MGS_GAAL2025.1.1 | GLO10 |
| 1 | certain | Identity of a feature can be determined using relevant observations and scientific judgment; therefore, one can be reasonably confident in the credibility of this interpretation. | FGDC-STD-013-2006 | GLO01 |
| 8 | contact | A plane or irregular surface between two different types or ages of rock, sediment or other geologic and stratigraphic units. | AGI_2011 | GLO07 |
| 7 | cross section | A plane or polyline along which a diagram is drawn showing the transected subsurface and topographic features and geology; specifically a vertical section drawn at right angles to the longer axis of a geologic feature. | AGI_2011 | GLO06 |
| 13 | DMU-Heading1 | Format for map unit headings. All capital letters with 18 pt Times New Roman font. | MGS_GAAL2025.1.1 | GLO12 |
| 6 | DMU Unit 1 | Style for map units, 12 pt Times New Roman font. This format is used for units mapped at the surface, and may or may not contain subunits. | MGS_GAAL2025.1.1 | GLO05 |
| 12 | DMU Unit 2 | 12 pt Times New Roman font. Units shown in cross section, but not in the map view. Units are either divided in the map view or are in the subsurface only. | MGS_GAAL2025.1.1 | GLO11 |
| 10 | fault | A discrete surface or zone of discrete surfaces separating two rock masses across which one mass has slid past the other. | AGI_2011 | GLO09 |
| 3 | High | The selected term in the GeoMaterial field (and its definition) adequately characterizes the overall lithologic nature of rocks and (or) sediments in the map unit. | GeMS_2020 | GLO03 |
| 4 | Medium | The selected term in the GeoMaterial field (and its definition) generally characterizes the overall lithologic nature of rocks and (or) sediments in the map unit, but one or more significant but minor lithologies are not adequately described by the selected term. | GeMS_2020 | GLO04 |
| 2 | questionable | Identity of a feature cannot be determined using relevant observations and scientific judgment; therefore, one cannot be reasonably confident in the credibility of this interpretation. For example, IdentityConfidence = questionable is appropriate when a geologist reasons "I can see some kind of planar feature that separates map units in this outcrop, but I cannot be certain if it is a contact or a fault." | FGDC-STD-013-2006 | GLO02 |
| 9 | water body | Perrenial natural or manmade area of surface water of adequate size to map, including streams, rivers, lakes, impoundments. | MGS_GAAL2025.1.1 | GLO08 |