Geologic units in Collin county, Texas

Austin Chalk (Late Cretaceous; Gulfian Series) at surface, covers 49 % of this area

Austin Chalk

Ozan Formation (Late Cretaceous; Gulfian Series) at surface, covers 19 % of this area

Ozan Formation

Marlbrook Marl (Late Cretaceous; Gulfian Series) at surface, covers 9 % of this area

Marlbrook Marl

Alluvium (Holocene) at surface, covers 8 % of this area

Alluvium

Eagle Ford Formation (Late Cretaceous) at surface, covers 6 % of this area

Eagle Ford Formation

Terrace deposits (Pleistocene and Holocene) at surface, covers 4 % of this area

Terrace deposits

Pecan Gap Chalk (Late Cretaceous; Gulfian Series) at surface, covers 3 % of this area

Pecan Gap Chalk

Wolfe City Formation (Late Cretaceous; Gulfian Series) at surface, covers 1.0 % of this area

Wolfe City Formation

Gober Chalk and Roxton Limestone (Late Cretaceous; Gulfian Series) at surface, covers 0.7 % of this area

Gober Chalk and Roxton Limestone

Neylandville Marl (Late Cretaceous; Gulfian Series) at surface, covers 0.2 % of this area

Neylandville Marl