GENERAL OUTCROP SECTION OF THE BLACK HILLS AREA FORMATION SECTION THICKNESS IN FEET DESCRIPTION QUATERNARY SANDS AND GRAVELS 0-50 Sand, gravel, and boulders PLIOCENE OGALLALA GROUP 0-200 Light colored sands and silts MIOCENE ARIKAREE GROUP 0-50 Light colored clays and silts White bed at base OLIGOCENE WHITE RIVER GROUP Brule Formation Chadron Formation 0-600 Light colored clays with sandstone channel fillings and local limestone lenses PALEOCENE FORT UNION FORMATION TONGUE RIVER MEMBER 0-425 Light colored clays and sands, with coal beds further north CANNONBALL MEMBER 1-225 Green MARINE shales and yellow sandstones; latter often as concretions LUDLOW MEMBER 0-350 So[?] gray clays and sandstones with beds of lignite. CRETACEOUS HELL CREEK FORMATION (Lance Formation) 425 Smoky colored soft brown shale and gray Sandstone, with thin lignite lenses in the upper part Lower half more sandy Many loglike concretions and thin lenses of iron carbonate FOX HILLS SANDSTONE 25-200 Grayish white to yellow sandstone Calc. PIERRE SHALE 1200-2000 Principal horizon of limestone lenses giving tepee buttes Dark gray shale containing scattered concretions. Widely scattered limestone masses, giving small tepee buttes. Black fissile shale with concretions. NIOBRA Formation 100-225 Impure chalk and calcareous shale CARLILE FORMATION Turner Sand Zone Wall Creek Sands 400-750 Light-gray shale with numerous large concretions and sandy layers Dark gray shale GREENHORN FORMATION (25-30) (200-350) Impure slabby limestone Weathers buff Dark gray calcareous shale, with thin Orman Lake limestone at base BELLE FOURCHE SHALE 300-450 Gray shale with scattered limestone concretions Clay sour bentonite at base MOWRY SHALE 150-250 Light-gray siliceous shale Fish scales and thin layers of bentonite NEWCASTLE SANDSTONE 20-60 Brown to light yellow and white sandstone SKULL CREEK SHALE 170-270 Dark gray to black shale. FALL RIVER [OAKOTA (?) S.S.] FUSON SHALE 10-200 Massive to slabby sandstone. MINNEWASTE LIMESTONE 10-188 Gray to purple shale Thin sandstones LAKOTA SANDSTONE 0-25 Massive gray limestone 25-485 Coarse, hard, crossbedded sandstone mostly buff to gray Conglomerate locally and coal at base MORRISON FORMATION 0-220 Green to maroon shale Thin sandstone. UNKPAPA SANDSTONE 0-225 Massive fine-grained sandstone. SUNDANCE FORMATION 250-450 Greenish-gray shale, thin limestone lenses. Glaucanitic sandstone; red xs near middle GYPSUM SPRING FORMATION 0-45 Red siltstone, gypsum, and limestone NUGGET (?) FORMATION 0-60 Massive crossbedded salmon sandstone TRIASSIC ? SPEARFISH FORMATION 300-700 Red sandy shale, soft red sandstone and siltstone with gypsum and thin limestone layers Gypsum locally near the base. PERMIAN MINNEKAHTA LIMESTONE 30-50 Massive gray, laminated limestone OPECHE FORMATION 50-135 Red shale and sandstone PENNSYLVANIAN MINNELUSA SANDSTONE 300-850 Yellow to red cross-bedded sandstone, limestone, and anhydrite locally at top Interbedded sandstone, limestone, dolomite, shale, and anhydrite Red shale with interbedded limestone and sandstone at base MISSISSIPPIAN PAHASAPA (MADISON) LIMESTONE 300-630 Massive light-colored limestone Dolomitic in part ENGLEWOOD LIMESTONE 30-60 Pink to buff limestone Shale locally at base ORDOVICIAN WHITEWOOD (RED RIVER) FORMATION 0-60 Buff dolomite and limestone WINNIPEG FORMATION 0-100 Green shale with siltstone at top and white sandstone at base CAMBRIAN DEADWOOD FORMATION 10-400 Massive to buff sandstone Greenish glauconitic shale, fraggy dolomite and flat-pebble limestone conglomerate Sandstone, with conglomerate locally at the base PRE-CAMBRIAN METAMORPHIC and IGNEOUS ROCKS Schist, slate, quartzite, and arkose grit Intruded by diorite, metamorphosed to amphibolite, and Sr granite and pegmatite