Geologic units in Washington county, Arkansas

Boone Formation (Early Mississippian- Meramecian to Osagean) at surface, covers 31 % of this area

Boone Formation

Pitkin Limestone, Fayetteville Shale (including the Wedington Sandstone member), and Batesville Sandstone (including the Hindsville Limestone Member) (Late Mississippian- Chesterian) at surface, covers 25 % of this area

Pitkin Limestone, Fayetteville Shale (including the Wedington Sandstone member), and Batesville Sandstone (including the Hindsville Limestone Member)

Atoka Formation, undivided (Middle Pennsylvanian- Atokan) at surface, covers 24 % of this area

Atoka Formation, undivided

Bloyd Shale, and Prairie Grove Member of the Hale Formation (Middle Pennsylvanian- Morrowan) at surface, covers 14 % of this area

Bloyd Shale, and Prairie Grove Member of the Hale Formation

Cane Hill Member of Hale Formation (Early Pennsylvanian- Morrowan) at surface, covers 5 % of this area

Cane Hill Member of Hale Formation

Chattanooga Shale (Lower Mississippian and Upper Devonian), Clifty Limestone (Middle Devonian), and Penters Chert (Lower Devonian) (Early Mississippian to Early Devonian) at surface, covers 0.6 % of this area

Chattanooga Shale (Lower Mississippian and Upper Devonian), Clifty Limestone (Middle Devonian), and Penters Chert (Lower Devonian)

Pitkin + Fayetteville + Hindsville + Moorefield Formations (Late Mississippian) at surface, covers < 0.1 % of this area

FORT SMITH- Mp "Pitkin Formation," limestone; "Fayetteville Formation," shale and limestone; "Hindsville Formation," limestone and shale; and "Moorefield Formation," limestone.

Atoka Formation (Middle Pennsylvanian) at surface, covers < 0.1 % of this area

TULSA- IPat "Atoka Formation," shale, siltstone, sandstone, and thin limestone. FORT SMITH- IPat "Atoka Formation," shale and sandstone. ARDMORE-SHERMAN- Shale, dark-gray, and sandstone, buff to white, fine- to coarse-grained, with some chert conglomerates; thickness, 800 to 3,000 feet. McALESTER TEXARKANA- Shale, gray to tan, illitic, chloritic, with many sandstones, fine- to coarse-grained, quartzose, micaceous, well- to poorly sorted; "Fanshawe" and "Red Oak Sandstones" in middle and "Spiro Sandstone" at base; thickness, 3,000 to 10,000 feet, increasing southeastward in subsurface, south of growth faults.

Keokuk and Reeds Spring Formations and St. Joe Group (Early Mississippian) at surface, covers < 0.1 % of this area

TULSA- "Keokuk Formation," chert and limestone. "Reeds Spring Formation," chert and limestone. "St. Joe Group," limestone and shale. FORT SMITH- Mkr "Keokuk Formation," chert; "Reeds Spring Formation," chert and limestone; and "St. Joe 'Group,'" limestone and marlstone.

Bloyd and Hale Formations (Early Pennsylvanian) at surface, covers < 0.1 % of this area

TULSA- "Bloyd Formation," limestone and shale. "Hale Formation," limestone and sandstone. FORT SMITH- IPbh "Bloyd Formation," shale and limestone; and "Hale Formation," limestone and sandstone.

Alluvium (Holocene) at surface, covers < 0.1 % of this area

WOODWARD- Lenticular and interfingering deposits of gravel, sand, silt, and clay. Generally light-tan to gray. Thickness along major streams ranges up to 100 feet and probably averages 40 feet; along minor streams the thickness ranges up to 45 feet and probably averages 20 feet. ENID- Sand, silt, clay, and locally gravel. Maximum thickness ranges from 30 to 80 feet (9 to 24 m) along major streams and from 0 to 60 feet (0 to 18 m) along minor streams. TULSA- Gravel, sand, silt, and clay. TULSA- Gravel, sand, silt, and clay. OKLAHOMA CITY- Sand, silt, clay, and lenticular beds of gravel. Thickness ranges from about 30 to 100 feet and probably averages about 50 feet along major streams. Along minor streams, thickness ranges from a few feet to about 50 feet and probably averages about 25 feet. LAWTON- Sand, clay, and gravel as much as 50 feet (15 m) thick; Shown only along major streams and tributaries. ARDMORE-SHERMAN- Gravel, sand, silt, and clay, including low terraces; thickness, about 25 to 100 feet. McALESTER TEXARKANA- Gravel, sand, silt, and clay, including low terraces about 30 feet above channels; thickness, about 50 feet along Little River and 110 feet along Red River.