Geologic Mapping of an Area Near Crook Creek, SD Purpose: To collect data necessary for the construction of a geologic map and cross-section of an area near Crook Creek, SD. This area contains several Paleozoic and Mesozoic units as well as modern alluvial and slump deposits. Some degree of folding has effected the area. Partner: Joe Smith South Dakota Study Area Crook City Quadrangle Field Station Data Type Structural Data CC-01 Mm Location S-D/Bed N35 o W, 20 o N CC S-D/Bed N38 o W, 16 o N Map Unit Data Structural Data Mapping Units Qal - Alluvium Qls - Land Slide T m - Minnelusa Ps - Spearfish Mm - Minnikata Osp - St. Peter R Osp 500 feet N20 O W of 6550 hill 1750 feet N30 O W of 6550 hill Benchmark: “X” atop 6550 hill near center of map Example Introduction and Data Table

Day 1 of Purpose: Working mostly the north 3 kilometers trying to ID major mapping units and collecting structural data. Weather: sunny ~65 o. Location: Parked vans near the two houses at the extreme north east edge of the mapping area. We will head ~ east on the dirt road. This road is labeled as a single dashed line. CC feet N20 o W BM there is an expose of Limestone along the northern side of the road. The outcrop is about 25’ long, 4‘ high in the middle, and tapers down at both ends. Bedding is thin, 1.5” – 2.5” and dipping Slightly to the north. The beds thicken with height. Rock Description: Fossiliferous Biomicrite of crinoids and brachiopods account for 5-10% of the rock and are matrix supported. This is the (Minnikata Formation) Lt. brn. on weathered surface, med. gray on fresh. Fossils 25’ 4’ E W “Cross-section along dirt road showing exposure of Minnikata limestone” S-D/Bed N35 o W, 20 o N Continuing ~east toward main north-south drainage valley. Should find exposure of older St. Peter Ss in valley. 20’ down into the valley at about the 1400’ contour line, CC-02 the soil becomes sandy. There is an outcrop of sandstone about another 30’ below. Looks like a good place for S-D. CC feet N30 o W of BM Outcrop of (St. Peter Ss). Nick point which exposes about 15 vertical feet over a length of 10’ at the bottom and narrowing to about 5 feet at the top. There are tangentially truncated cross-beds which range in thickness from 1.5’ to 2.0’ with the thinner beds near the top. The upper most bed is oxidized dark brown and provides a resistant ledge. Rock Description: St Peter Ss Weathered surface is med. brn, fresh is light yellow. All Stratigraphic Column of St. Peter Ss exposure near valley bottom NS 15’ grains are frosted. S-D/Bed N38 o W, 16 o N Well rndd, well srtd, med. grnd, calcareous Q-arenite. Note: Beds thicken higher in this outcrop feet N35 o W of BM Example Field Notes for Geologic Mapping

Example Stratigraphic Column