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Willis Formation

Willis Formation
StateTexas
NameWillis Formation
Geologic agePhanerozoic | Cenozoic | Tertiary | Pliocene
Original map labelPow
CommentsClay, silt, sand, siliceous granule to pebble gravel, some petrified wood; sand coarser than younger units, noncalcareous; deeply weathered, locally cemented by iron oxide; fluvitile; forms north-facing scarp. On Seguin Sheet (1974) thickness 100+- ft. On Austin 4 x 6-degree sheet (Moore and Wermund, 1993) unit consists of 1) channel facies--alluvial pebble gravel and sand, lt. gray to orange-brown, orange, gravelly coarse to fine sand which lenses of red, sandy silt and white to gray clay 10-60 m thick, pebbles mostly quartz, some chert and petrified wood, and 2) overbank facies--alluvial silt and clay made of brown, yellow, orange, fine silt and clay are intermixed and interbedded. 5-50+m thick.
Primary rock typeclay or mud
Secondary rock typesilt
Other rock typessand; gravel
Lithologic constituents
Major
Unconsolidated > Fine-detrital (Alluvial)
Unconsolidated > Coarse-detrital (Alluvial)
Minor
Unconsolidated > Coarse-detrital > Gravel (Bed)
Map references
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references
Moore, D.W. and Wermund, E.G., Jr., 1993a, Quaternary geologic map of the Austin 4 x 6 degree quadrangle, United States: U.S. Geological Survey Miscellaneous Investigations Series Map I-1420 (NH-14), scale 1:1,000,000.
Geographic coverageAustin - Bastrop - Colorado - DeWitt - Fayette - Gonzales - Grimes - Guadalupe - Harris - Hays - Jasper - Lavaca - Liberty - Montgomery - Newton - Polk - Sabine - San Jacinto - Tyler - Victoria - Walker - Waller - Washington

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