# Catskill Formation Canonical page: https://lithomap.app/resources/geologic-formations/united-states/catskill-formation Last reviewed: September 17, 2026 Page purpose: Comprehensive United States geologic formation reference for human readers, search systems, and language models. Major region: Appalachians Regional setting: Appalachian Basin Age: Late Devonian Age detail: Mostly Late Devonian; upper limits and rank vary regionally Depositional setting: River channels, floodplains, deltas, and coastal lowlands Rock types: Red sandstone, Siltstone, Shale, Conglomerate States in recognized usage: Maryland, New York, Pennsylvania, West Virginia ## Summary The Catskill Formation is a thick Appalachian red-bed succession built by rivers carrying sediment westward from rising Acadian mountains during Late Devonian time. ## Distribution Catskill-named rocks occur through Pennsylvania and adjoining New York, Maryland, and West Virginia. They form ridges, plateaus, and red-soil lowlands depending on sandstone content and structural position. Dozens of regional members divide the formation, and some surveys use Catskill as part of a larger group or red-bed interval. The base and top can also shift in age as river and marine facies intertongue across the basin. ## Geological history Rivers flowing from the Acadian highlands spread sand and mud across broad floodplains and deltas. Channel sandstone, overbank siltstone, floodplain shale, and local conglomerate record repeated migration of those river systems. Oxidation of iron in well-drained sediment produced the characteristic red color, while gray-green beds mark different groundwater or depositional conditions. Rapid sediment supply limited marine influence across much of the red-bed tract. ## Fossil record Plant fragments, fossil wood, fish remains, and freshwater or brackish-water organisms occur locally. Some beds are nearly barren, while transitional intervals closer to marine strata can preserve a more varied fauna. The scarcity of fossils in many red beds is meaningful but not absolute. Oxidizing floodplain soils and energetic channels were generally less favorable for preservation than quiet ponds or marginal-water settings. ## Minerals and geological resources Quartz is abundant in sandstone, with feldspar, mica, and clay minerals in finer beds. Hematite and related iron oxides create red pigmentation; calcite or silica may cement resistant sandstone. Quartz pebbles are common in conglomeratic members. The unit is not uniformly mineralized, and red color alone does not indicate an iron-ore deposit. ## Field context - Member names and the Catskill–Chemung transition differ across the Appalachian Basin. - Sandstone ledges can overhang softer shale and release blocks along joints. - Red soil or float rock is not sufficient for a formation identification without bedrock context. ## Connected field guides - Sandstone (rock; Named rock type and mineral context) — https://lithomap.app/resources/rock-identification/sandstone - Conglomerate (rock; Named rock type) — https://lithomap.app/resources/rock-identification/conglomerate - Shale (rock; Named rock type) — https://lithomap.app/resources/rock-identification/shale - Siltstone (rock; Named rock type) — https://lithomap.app/resources/rock-identification/siltstone - Calcite (mineral; Mineral discussed in this formation) — https://lithomap.app/resources/mineral-identification/calcite - Feldspar (mineral; Mineral discussed in this formation) — https://lithomap.app/resources/mineral-identification/feldspar Mapped location and formation context support an identification but cannot establish one. Compare several physical properties and use laboratory analysis when the material remains ambiguous. ## Connected state geology guides - Pennsylvania geology — https://lithomap.app/resources/geology/united-states/pennsylvania ## Authoritative sources - Geolex Catskill unit record — U.S. Geological Survey: https://ngmdb.usgs.gov/Geolex/Units/Catskill_927.html - Catskill depositional interpretation and regional geology — U.S. Geological Survey: https://pubs.usgs.gov/gf/174/text.pdf ## Formation photograph - Image: https://lithomap.app/_delivery/formations/catskill-formation.webp - Description: Red Catskill Formation rocks exposed along Horseshoe Curve in Pennsylvania - Creator: James Stuby - License: Public domain — https://creativecommons.org/publicdomain/mark/1.0/ - Source record: https://commons.wikimedia.org/wiki/File:Catskill1.jpg Formation-level information does not prove that a fossil or mineral occurs at a specific coordinate. It also does not establish ownership, access, collecting permission, present conditions, or specimen identity.