Mississippi Office of Geology
Open-File Report 365
GEOLOGIC MAP of the BENTONIA
7.5-Minute QUADRANGLE
Madison and Yazoo Counties, Mississippi
2026
Geology by 
Timothy J. Palmer, RPG, Jonathan R. Leard, PhD, RPG,
James E. Starnes, RPG, and Natalya S. Usachenko, GIT  
Mississippi Department of Environmental Quality
Mississippi Office of Geology - Surface Mapping Division
Mississippi Geological Survey
700 North State Street
Jackson, Mississippi 39225
Copyright  © 2026 Mississippi Department of Environmental Quality, Office of Geology

Mississippi Department of Environmental Quality
Office of Geology Surface Mapping Division
Mississippi Geological Survey
GEOLOGIC MAP OF THE 7.5-MINUTE 
BENTONIA QUADRANGLE
OPEN-FILE REPORT 365
Prepared in cooperation with
UNITED STATES GEOLOGICAL SURVEY
NATIONAL COOPERATIVE GEOLOGIC MAPPING PROGRAM
Correlation of Map Units
Base map produced by the Mississippi Office of Geology
PCS: NAD 1983 UTM Zone 15N
GCS:GCS NORTH AMERICAN 1983
Projection: Transverse Mercator
Datum: North American 1983
Units: Meter
Declination: USGS MS Bentonia 2024 Topographic Map
MDEM base map data from MARIS
Borehole data from Mississippi Office of Geology.

Field Photographs
Paleoindian and transitional Early Archaic chert artifacts dating back to the late Pleistocene and early Holocene manufactured from Pre-loess Terrace gravels collected by Donald Hearn from site 22YZ937 on the alluvial plain of Walesheba Creek and documented by Survey Geologist James Starnes.
Loess derived stream alluvium with a bedload quartz sand derived from the Pre-loess Terrace deposits exposed along the active channel of Walesheba Creek in Section 21, Township 10 North, Range 1 West.
A thick humus bed of well-preserved lignitic macroflora fossils including woody debris, leaves, and seeds in late Pleistocene alluvial loess exposed along the active channel of Indian Creek in Section 16, Township 10 North, Range 1 West.
Closeup of a thick humus bed of well-preserved lignitic macroflora fossils including the remains of logs, leaves, river cane, seeds and seed pods in an alluvium exposed along the active channel of Indian Creek in Section 16, Township 10 North, Range 1 West.
Partial fossil of right mandible of American mastodon Mammut americanum donated by  J.P. Ketchum, Tylnn Sanders, and Braden Scott found in association of a thick humus bed exposed along the active channel of Indian Creek in Section 16, Township 10 North, Range 1 West.
Survey geologist James Starnes measuring a vertical section of late Pleistocene Peorian loess deposits in Section 2, Township 10 North, Range 2 West.
Panorama of fluvial sands and gravels of ancestral Mississippi River Pre-loess Terrace deposits in an inactive gravel pit exhibiting a perched water table with the underlying clays of the Yazoo Formation forming an aquitard in Section 11, Township 10 North, Range 2 West.
Survey geologist James Starnes measuring a vertical section of late Pleistocene Peorian loess deposits unconformably overlying fluvial sands and gravels of ancestral Mississippi River Pre-loess Terrace deposits in an active gravel pit in Section 11, Township 10 North, Range 2 West.
Loess derived alluvium unconformably overlying deeply weathered montmorillonitic clays of the marine Yazoo Formation exposed along the active channel of Cypress Creek in Section 23, Township 10 North, Range 1 West.
Deeply weathered montmorillonitic clays of the marine Yazoo Formation exposed along Myrtle Road in Section 24, Township 10 North, Range 1 West.

Descriptions of Map Units
Alluvium (Pleistocene to Holocene) 
Sand, yellow- to brownish-white in color, fine- to coarse-grained, subrounded to rounded, predominately quartzose, silty, clayey; humus lenses common. Streams on clay subcrop will exhibit shallow, wide alluvial plains while streams on sand subcrop tend to incise creating steep valleys with narrow alluvial plains, silicified wood common. Thickness approximately 15 feet along larger streams, thinning up tributaries.
Stream Terrace (Pleistocene to Holocene)
Fluvial deposits associated with base elevation change with the incision of the Pearl River during the Pleistocene epoch just west of French's Store; Sand, yellow- to brownish-white in color, fine- to coarse-grained, subrounded to rounded, predominately quartzose, locally graveliferous, silty to clayey; humus lenses common. Silicified wood may be common.
Loess (Pleistocene)
Silt, buff to tan, pale yellow, red, gray to gray-green where in anoxic conditions, quartzose to feldspathic. Loess is considered an eolian deposit derived from glacial outwash. Loess is typically calcareous with dolomite and calcite; however, the upper portion of the loess can be deeply weathered, leached / noncalcareous, and has been commonly referred to as "brown loam." Loess deposits unconformably blanket the pre-loess topography with substantial local variations in thickness but generally thickening towards the west. In places, weathered loess contains secondary deposits of small calcareous concretions such as caliche and loess dolls. Loess can be locally and sparingly fossiliferous, commonly containing tests or steinkerns of pulmonate gastropods and less commonly containing fossils of Pleistocene vertebrates.
Pre-loess Terrace Deposits (Pleistocene)
Pleistocene ancestral Mississippi River terraces deposited prior to Pleistocene loessification. Sand, yellow, orange, purple, red, pink, fine- to coarse-grained, predominantly quartzose, cross-bedded to massive; graveliferous, pea to large cobble size clasts, boulder size ice-rafted clasts of sandstone and chert. Economically significant gravels are predominantly chert with lesser amounts of vein quartz, metaquartzite, agate, sandstone, and rare rhyolite clasts; clay, pink to white, generally occurring as discontinuous lenses and as rip-up clasts up to boulder-size. Conglomeratic ironstone ledges are common in the graveliferous sands at the base of the deposits. The base of this terrace occurs at approximately 250 ft MSL and is masked by about 40 ft of loess overburden. 
Jackson Group
Yazoo Formation (Eocene to Oligocene) 
Outer neritic to bathyal marine clay. Clay is calcareous and montmorillonitic, blue- green when unweathered. Sparingly fossiliferous, with marine mollusk shell hash common along partings. Bentonite seams present. Limestone ledges occur in places. The Yazoo Formation is marked by the planktonic foraminifera Hantkenina alabamensis. The Yazoo Formation conformably overlies the Moodys Branch Formation. Total thickness is approximately 400 ft.
Cross Section Units Not Exposed at the Surface
Moodys Branch Formation (Eocene)
The Moodys Branch Formation is the basal member of a marine transgression towards the close of the Eocene epoch in the northern Gulf, situated unconformably above the deltaic to estuarine Cockfield Formation and conformably below the outer neritic to bathyal clays of the Yazoo Formation. It consists of sandy, fossiliferous marl containing abundant marine mollusk shells  of the genera Glycymeris and Venericardia. The unit unconformably overlies the Cockfield Formation, reflecting the delta destructional phase and subsequent marine transgression, and it conformably grades upward into the Yazoo Formation. Total thickness is approximately 15 ft.
Claiborne Group
Cockfield Formation (Eocene)
Deltaic to estuarine deposits dominated by clays in the upper portions of the formation and sands in the lower portion. Clays are gray to brown in color, silty to fine sandy, plastic, highly carbonaceous with thin beds of lignite common, slightly micaceous, and locally pyritic. Sands are quartzose and are cross bedded to massive, locally lignitic, and can be silty to clayey. Conformably overlies the Cook Mountain Formation. Thickness is approximately 400 feet.
Cook Mountain Formation (Eocene)
Marine clays, silts, and sands. Clay, chocolate brown in color. Silt, dark yellowish-brown, carbonaceous, clayey, glauconitic, micaceous, sandy. Sand, light-gray to grayish-brown, fine- to coarse-grained, quartzose, fossiliferous, silty, clayey, micaceous, carbonaceous; shaley in upper portions, cross bedded in lower portions. Unconformably overlies the Kosciusko Formation. Thickness is approximately 60 feet.

Adjoining 7.5' Quadrangles

Geologic maps are only a guide to current understanding and do not 
eliminate the need for detailed investigations of specific sites for specific 
purposes. The views and conclusions contained in this Open-File Report 
are those of the geologists and should not be interpreted as representing 
the official policies, either expressed or implied, of the State of 
Mississippi or of the United States Government.

LIDAR derived Bare Earth Hillshade