SYSTEM SERIES STAGE FORMATION MEMBER THICKNESS (FEET) LITHOLOGY TOPOGRAPHIC EXPRESSION NEOGENE PLEISTOCENE Recent Alluvium 0-70 Silt, sand, gravel Present channel and flood plain; surface of lowest terrace. Wisconsinan a. Low b. Big- terrace nell a. 0-100 Silt, sand, gravel Low terraces lying approximately 15 to 20 feet above Smoky Hill and Saline Rivers. depos- (Brady its Soil) c. Peoria b. 0-2? Loess Thin mantle on upland Loess Thin mantle on upland Illinoisan (Sangamon Soil) Loveland c. 5-60 Loess; laminated sand and silt Thin mantle on upland grading laterally into stream-laid deposits in upper part of Kansan-Illinoisan high-terrace complex. Crete 0-65 Sand and gravel Widely distributed in dissected Kansan-Illi-noisan high-terrace complex. Kansa: Sappa 0-45 Silt and sandy silt with lenses of sand, gravel, and volcanic ash (Pearlette ash bed) Channel deposits truncated by overlying Illinoisan deposits in high-terrace complex. Grand Island 0-35 Sand and gravel Basal part of channel deposit underlying the high-terrace complex. Nebraska: Holdrege 0-25 Gravel Channel deposits lying high on valley walls or on divides between major streams in Russell and Ellis counties. Pliocene Ogallala 0-226 Chiefly sand, with clay, silt, and gravel; in part lime-cemented to form "Mortar beds," in part cemented with silica to form "quartzite." Also contains some chert, bentonitic clay, volcanic ash, and limestone. Loess-mantled cap rock of upland surface of High Plains. Outlying remnants cap divides in highly dissected areas. Exposed in steep bluffs and cliffs at upland margin along larger stream courses. CRETACEOUS GULFIAN CAMPAANIAN Weskan Shale 170 Dark-gray shale with clay-ironstone and limestone concre-tions, phosphate nodules, and bento-nite. Canyons and slopes in valleys of larger streams; local badlands. Pierre Shale Sharon Springs Shale 155 Dark-gray shale, organic-rich in upper part, with phosphate nodules, limestone concre-tions, calcareous septarian concre-tions, and many thin seams of bentonite. Canyons and slopes in valleys of larger streams; commonly forms badlands. CONIACIAN-SANTONIAN ? Smoky Hill Chalk 560-620 Olive-gray shaly chalk mostly weather-ing grayish orange and yellowish gray; many thin seams of bentonite. Where in-tensely weathered lacks shaly struc-ture and forms re-sistant cap rock. Canyons and badlands along valley walls of larger streams. Many rock pinnacles. Niobrara Chalk Fort Hays Lime-stone 55-75 Light-olive-gray chalky limestone, mostly weathering pale grayish orange, yellowish gray, or nearly white. Cliffs along valley walls of large streams. Cap rock on buttes, mesas, and low bluffs. 10