# United States Geologic Formations

Canonical page: https://lithomap.app/resources/geologic-formations/united-states
Last reviewed: September 18, 2026
Page purpose: Directory for LithoMap's 36-page foundation collection of comprehensive United States geologic formation guides.

The foundation is geographically balanced: six dedicated formation pages in each of six major U.S. regions. Every page covers location, age, depositional history, rock types, fossil record, minerals and geological resources, field context, terminology limits, authoritative scientific sources, and a reusable formation photograph with complete creator and license information. Each guide has an isolated canonical URL.

The collection page also provides a supplemental interactive United States geology map. A selected vector-tile unit is shown immediately; the source service may add detail when available. A keyboard-accessible control inspects the unit at the map center, failed map loads can be retried, and completed editorial profiles link to their isolated canonical guides. The map is approximate and does not establish specimen identity, ownership, access, hazards, or collecting permission.

## Pacific Coast

- John Day Formation — Late Eocene to early Miocene — https://lithomap.app/resources/geologic-formations/united-states/john-day-formation
- Clarno Formation — Eocene — https://lithomap.app/resources/geologic-formations/united-states/clarno-formation
- Ohanapecosh Formation — Late Eocene to Oligocene — https://lithomap.app/resources/geologic-formations/united-states/ohanapecosh-formation
- Monterey Formation — Miocene — https://lithomap.app/resources/geologic-formations/united-states/monterey-formation
- Crescent Formation — Early to middle Eocene — https://lithomap.app/resources/geologic-formations/united-states/crescent-formation
- Siletz River Volcanics — Paleocene to early Eocene — https://lithomap.app/resources/geologic-formations/united-states/siletz-river-volcanics

## Colorado Plateau / Rockies

- Morrison Formation — Late Jurassic — https://lithomap.app/resources/geologic-formations/united-states/morrison-formation
- Green River Formation — Eocene — https://lithomap.app/resources/geologic-formations/united-states/green-river-formation
- Chinle Formation — Late Triassic — https://lithomap.app/resources/geologic-formations/united-states/chinle-formation
- Kaibab Formation — Early Permian — https://lithomap.app/resources/geologic-formations/united-states/kaibab-formation
- Florissant Formation — Late Eocene — https://lithomap.app/resources/geologic-formations/united-states/florissant-formation
- Navajo Sandstone — Early Jurassic — https://lithomap.app/resources/geologic-formations/united-states/navajo-sandstone

## Great Plains

- Hell Creek Formation — Latest Cretaceous — https://lithomap.app/resources/geologic-formations/united-states/hell-creek-formation
- Niobrara Formation — Late Cretaceous — https://lithomap.app/resources/geologic-formations/united-states/niobrara-formation
- Dakota Sandstone — Early to early Late Cretaceous — https://lithomap.app/resources/geologic-formations/united-states/dakota-sandstone
- Pierre Shale — Late Cretaceous — https://lithomap.app/resources/geologic-formations/united-states/pierre-shale
- Ogallala Formation — Miocene to Pliocene — https://lithomap.app/resources/geologic-formations/united-states/ogallala-formation
- Fox Hills Sandstone — Latest Cretaceous — https://lithomap.app/resources/geologic-formations/united-states/fox-hills-sandstone

## Midwest / Great Lakes

- Trenton Limestone — Middle to Late Ordovician — https://lithomap.app/resources/geologic-formations/united-states/trenton-limestone
- New Albany Shale — Late Devonian to earliest Mississippian — https://lithomap.app/resources/geologic-formations/united-states/new-albany-shale
- Maquoketa Shale — Late Ordovician — https://lithomap.app/resources/geologic-formations/united-states/maquoketa-shale
- St. Peter Sandstone — Middle Ordovician — https://lithomap.app/resources/geologic-formations/united-states/st-peter-sandstone
- Eau Claire Formation — Late Cambrian — https://lithomap.app/resources/geologic-formations/united-states/eau-claire-formation
- Mount Simon Sandstone — Late Cambrian — https://lithomap.app/resources/geologic-formations/united-states/mount-simon-sandstone

## Appalachians

- Marcellus Shale — Middle Devonian — https://lithomap.app/resources/geologic-formations/united-states/marcellus-shale
- Catskill Formation — Late Devonian — https://lithomap.app/resources/geologic-formations/united-states/catskill-formation
- Lock Haven Formation — Late Devonian — https://lithomap.app/resources/geologic-formations/united-states/lock-haven-formation
- Pocono Formation — Early Mississippian — https://lithomap.app/resources/geologic-formations/united-states/pocono-formation
- Tuscarora Formation — Latest Ordovician to Early Silurian — https://lithomap.app/resources/geologic-formations/united-states/tuscarora-formation
- Onondaga Limestone — Middle Devonian — https://lithomap.app/resources/geologic-formations/united-states/onondaga-limestone

## Gulf / Atlantic

- Ocala Limestone — Late Eocene — https://lithomap.app/resources/geologic-formations/united-states/ocala-limestone
- Suwannee Limestone — Oligocene — https://lithomap.app/resources/geologic-formations/united-states/suwannee-limestone
- Castle Hayne Limestone — Middle to late Eocene — https://lithomap.app/resources/geologic-formations/united-states/castle-hayne-limestone
- Yorktown Formation — Pliocene — https://lithomap.app/resources/geologic-formations/united-states/yorktown-formation
- Calvert Formation — Early to middle Miocene — https://lithomap.app/resources/geologic-formations/united-states/calvert-formation
- Citronelle Formation — Pliocene to possible early Pleistocene — https://lithomap.app/resources/geologic-formations/united-states/citronelle-formation

Future growth is planned in balanced batches of 12 pages, ideally two per region. The initial editorial ceiling is approximately 120 pages; expansion beyond that requires evidence from search demand or user activity. LithoMap does not publish automatically generated thin formation pages.

Rock type, thickness, fossils, minerals, member names, boundaries, and formal stratigraphic rank may vary across a formation's range. A named formation does not guarantee that a fossil or collectible mineral is present at a particular location.