Geologic units in Mobile county, Alabama

Alluvial, coastal and low terrace deposits (Holocene) at surface, covers 36 % of this area

Varicolored fine to coarse quartz sand containing clay lenses and gravel in places. Gravel composed of quartz and chert pebbles and assorted metmorphic and igneous rock fragments in streams near the Piedmont. In areas of the Valley and Ridge province gravel composed of angular to subrounded chert, quartz, and quartzite pebbles. Coastal deposits include fine to medium quartz sand with shell fragments and accessory heavy minerals along Gulf beaches and fine to medium quartz sand, silt, clay, peat, mud and ooze in the Mississippi Sound, Little Lagoon, bays, lakes, streams, and estuaries.

Citronelle Formation (Pleistocene-Pliocene) at surface, covers 34 % of this area

Moderate-reddish-brown deeply weathered fine to very coarse quartz sand and varicolored typically mottled lenticular beds of clay and clayey gravel. Limonite pebbles and lenses of limonite cemented sand occur locally in weathered exposures. Gravel is composed of chert and quartz pebbles.

Miocene Series undifferentiated (Miocene) at surface, covers 30 % of this area

Moderate-yellowish-orange thin-bedded to massive fine to coarse sand, gravelly sand, thin-bedded to massive clay and sandy clay. Clays are plastic in part. Limonite pellets occur in places along clay-sand contacts. Gravel is composed of quartz and chert granules and pebbles. Locally the upper part of the unit is Pliocene in age.

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

Loam, sand, gravel and clay.

Citronelle formation (Pleistocene) at surface, covers < 0.1 % of this area

Red sand and gravel and white clay; may be of Pliocene age; the formation mapped is equivalent to the Willis sand and does not include the terrace deposits, colluvium, and residuum commonly considered "Citronelle".

High terrace deposits (Pleistocene) at surface, covers < 0.1 % of this area

Varicolored lenticular beds of poorly sorted sand, ferruginous sand, silt, clay, and gravelly sand. Sand consists primarily of very fine to very coarse poorly sorted quartz grains; gravel composed of quartz, quartzite, and chert pebbles.