Crook Creek, SD

1. Crook Creek, SD 5-22-07 Collect data for geologic map and cross-sections. Partner: Joe Smith Structural Data Mapping Units Study Area Qal - Alluvium Qls - Land Slide T m - Minnelusa Ps - Spearfish Mm - Minnikata Osp - St. Peter South Dakota R Crook City Quadrangle Structural Data Map Unit Location Data Type Data Field Station 500 feet N20OW of 6550 hill N35oW, 20oN 352410 4911320 S-D/Bed CC-01 Mm 1750 feet N30OW of 6550 hill CC-03 N38oW, 16oN 352650 4911810 S-D/Bed Osp

2. Day 1 of 3 5-22-07 Work mostly the north 3 kilometers. Weather is sunny ~65o. Continuing ~east toward main north-south drainage valley. Should Parked vans near the two houses at the extreme north east edge of the find exposure of older St. Peter Ss in valley. mapping area. We will head ~ east on the dirt road. This road is labeled as a single dashed line. CC-02 20’ down into the valley at about the 1400’ contour line, the soil becomes sandy. There is an outcrop of sandstone CC-01 ~ 350’ N85oE of western most house there is an expose of about another 30’ below. Looks like a good place for S-D. Limestone along the northern side of the road. The outcrop S-D/Bed is about 25’ long, 4‘ high in the middle, and tapers down at CC-03 Outcrop of (St. Peter Ss) 1250’ N15oW of 1640’ hill. This is a N35oW, 20oN both ends. Bedding is thin, 1.5” – 2.5” and dipping to the nick point which exposes about 15 vertical feet over a length S-D/Bed of 10’ at the bottom and narrowing to about 5 feet at the top. Slightly to the north. The beds thicken with height. N38oW, 16oN There are tangentially truncated cross-beds which range in thickness from 1.5’ to 2.0’ with the thinner beds near the top. Rock Description: Fossiliferous Biomicrite The upper most bed is oxidized dark brown and provides a resistant ledge. Lt. brn. on weathered surface, med. gray on fresh. Fossils of crinoids and brachiopods account for 5-10% of the rock Rock Description: St Peter Ss Well rndd, well srtd, med. grnd, calcareous Q-arenite. and are matrix supported. This is the (Minnikata Formation) Weathered surface is med. brn, fresh is light yellow. All grains are frosted. “Cross-section along dirt road showing exposure of Minnikata limestone” N S E W Stratigraphic Column of St. Peter Ss exposure near valley bottom 4’ 15’ 25’