Willis Formation (TXPOw;0)

State	Texas
Name	Willis Formation
Geologic age	Phanerozoic \| Cenozoic \| Tertiary \| Pliocene
Original map label	Pow
Comments	Clay, 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 type	clay or mud
Secondary rock type	silt
Other rock types	sand; 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. [http://pubs.er.usgs.gov/publication/i1420(NH14)]
Geographic coverage	Austin - Bastrop - Colorado - DeWitt - Fayette - Gonzales - Grimes - Guadalupe - Harris - Hays - Jasper - Lavaca - Liberty - Montgomery - Newton - Polk - Sabine - San Jacinto - Tyler - Victoria - Walker - Waller - Washington