Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-33, PART A MINNESOTA GEOLOGICAL SURVEY THE HOUSTON COUNTY BOARD OF COMMISSIONERS, AND Houston County Harvey Thorleifson, Director the Minnesota Legacy Amendment'S Clean Water Fund Plate 2—Bedrock Geology 91° 22' 30" W. 91° 37' 30" W. 91° 30' W. LA CROSSE WINONA COUNTY R. 7 W. B R. 6 W. R. 5 W. R. 4 W. FILLMORE COUNTY COUNTY Looney Pine 300 Pine Creek lr ¤61 300 350 D Creek 2 350 1 300 6 1 6 U 1 6 BEDROCK GEOLOGY 6 Ops 76 Creek U ) U D 350 ¤14 Creek w 250 300 w D 300 Money 250 s 300 250 U 350 Mississippi Opo 200 D Silver La Crescent Opo e By FILLMORE COUNTY Blue 350 Ops j 300 300 Lake CORRELATION OF MAP UNITS s 350 Ops Pine Julia R. Steenberg j Creek lr Oc 350 Ops 350 Creek Storer Day MONEY CREEK 350HOUSTON 250 MOUND PRAIRIE LA CRESCENT )16 T. 104 N. Od Upper Ordovician T. 104 N. 2014 Root 250 350 M m Opg Creek River lr 300 Creek Target River 250 350 Silver Lake 300 w LOCATION DIAGRAM Os 300 350 Middle Ordovician 250 Creek 250 300 D 300 91° 15' W. M U 250 Root e Ops e 300 300 e River m River unconformity Creek 350 lr R Lower Ordovician o o 250 250 Root River t Opo Root M 300 R ive PALEOZOIC Ferndales r unconformity 31 w 36 31 w 36 31 36 31 36 31 e D lr 350 )16 250 )16 Mound j MAP SYMBOLS U 200 River Creek 350 250 300 s Geologic contact—Approximately located. Lithostratigraphic Creek Houston HOKAH WISCONSIN unit 6 1 6 Prairie 1 D6 U 1 Composite natural gamma log Root 250 )26 Fold—Axial trace of anticline, syncline. Fold limbs typically have Ops 1 6 Crystal Creek Hokah Upper Cambrian Era Lithology 350 350 300 300 Increasing count 43° 45' N. j )76 250 43° 45' N. lr F shallow dips and are inferred from subsurface data. Group, Creek Formation, Daley 300 300 Creek M 0 100 300 350 System-Series Fault—Faults are inferred from abrupt changes in the elevation of Map symbol Hydrostratigraphic properties unconformity Member API-G units Thickness (in feet) Swede )44 Bottom w 300 stratigraphic units from subsurface and outcrop data. Letters 300 350 350 Opo 350 Fork Opo w indicate relative vertical displacement: U—up, D—down. 300 Opo Lawrence e 350 Cummingsville Creek Lake Location of geologic cross section Oc Thompson Middle Cambrian A LA CROSSE A' Formation > 80 m Ops South Badger 250 Opo lr COUNTY Location of bedrock outcrop lr U 200 unconformity D Galena Group VERNON 300 Butterfield Ops Decorah 350 U COUNTY pC PRECAMBRIAN Od YUCATAN SHELDON UNION 350 Shale 30-35 T. 103 N. e 350 350 T. 103 N. Upper Ordovician 350 Beaver D Bridge Spring Platteville and Crystal 300 Opg 350 350 Glenwood Formations 30-35 s Branch Ph 300 350 Creek 350 j 300 Creek350 Creek 250 350 F Creek F Creek 300 St. Peter Os j Creek Brownsville Sandstone INTRODUCTION DESCRIPTION OF MAP UNITS 70-90 BROWNSVILLE Middle Odrovician 300 River The geologic map on this plate depicts the type, distribution, and structure of the bedrock Galena Group w w Indian Spring 350 250 e Root M Creek units in Houston County that are either exposed at the land surface or lie directly beneath w Sullivan Oc Cummingsville Formation (Upper Ordovician)—Limestone interbedded with Wildcat 250 unconsolidated Quaternary sediments of variable thickness (see cross sections and Plate 3, shale. The limestone is yellowish-gray to yellowish-brown, shaley, fossiliferous, Fork Sheldon 36 31 31 36 31 M j 36 31 35 Surficial Geology). The map shows how the bedrock surface would appear if it were viewed from Shakopee and fine-grained with thin and crinkly bedding. The shale is green to gray and Formation Ops 350 Willow River an aerial perspective and the overlying Quaternary sediments were stripped away. The bedrock calcareous. Exposures weather to a serrated profile because of the alternating 90-120 Creek New Creek units near the land surface in Houston County consist of sedimentary rocks of Paleozoic age that Richmond 300 shale beds. Unit forms ledges where it caps small plateaus in southwest Houston lr lr 6 350 250 Ops 6 form distinguishable and mappable layers designated as formations. These units are commonly County. Thickness exceeds 80 feet (24 meters) locally. 1 6 U 1 6 1 2 South D exposed in bluffs, riverbanks, rock quarries, and roadcuts throughout the county. Some of these 350 Decorah Shale (Upper Ordovician)—Fossiliferous green-gray shale with thin LITHOLOGY KEY 350 )44 Od Brownsville Beaver 350 formations are major reservoirs for the water supply in the county and a major source of aggregate Riceford interbeds of yellowish-gray fossiliferous limestone. Limestone beds are more 350 for construction materials. Opo abundant at the base. The maximum thickness ranges from 30 to 35 feet (9 to 11 Limestone )76 350 Ops 300 Ops The production of the map and associated products relied on several different data sources, meters). Creek F including outcrops, water-well and scientific drilling records, drill cuttings, borehole geophysical Lower Ordovician Opg Platteville and Glenwood Formations, undivided (Upper Ordovician)—The Dolostone Prairie du Chien Group Oneota 300 300 logs, and previously published geologic maps of Houston and adjacent counties (Mossler and Opo s Platteveille Formation is fossiliferous, thin- to medium-bedded, light gray to tan, Dolomite Hager City 170-200 East e Book, 1984; Olsen, 1988; Mossler, 1995; Runkel, 1996, 2001; Evans, 2003). The somewhat 350 Sandy dolostone Opo )26 finely crystalline limestone with thin gray shale partings. Quartz sand grains and irregular distribution and density of data can be seen on Plate 1, Data-Base Map, and this should dark phosphate clasts are present at the base. Unit forms ledges where it caps 300 Sandstone 200 be considered when assessing the reliability of the map at any particular location. Areas with a small plateaus in southwest Houston County. Maximum thickness ranges from 25 BLACK HAMMER CALEDONIA MAYVILLEj Very fine- to fine-grained T. 102 N. U Caledonia T. 102 N. high density of bedrock control points are more likely to have an accurate interpretation of the 300 350 to 30 feet (8 to 9 meters). The Glenwood Formation is sandy, green-gray shale. j 300 D 300 350 bedrock geology, whereas those areas with widely spaced control points may be less reliable and 43° 37' 30" N. North s 43° 37' 30" N. It contains dark phosphatic grains throughout. Thin, fine- to coarse-grained, Coon Fine- to medium-grained Valley G 350 inappropriate for site-specific needs. Characteristics of each formation are given in the stratigraphic quartzose sandstone lenses are common. The maximum thickness ranges from 3 350 350 column (Fig. 1) and in the description of map units. The accompanying bedrock geologic cross 350 Fork to 6 feet (1 to 2 meters). Medium- to coarse-grained Riceford Creek sections add the dimension of depth and illustrate the stratigraphic, structural, and topographic 300 West Os St. Peter Sandstone (Upper and Middle Ordovician)—Mostly fine- to medium- Jordan 350 CROOKED CREEK Mississippi relationships of the bedrock units; as well as the variable thickness of the overlying Quaternary j Opo Crooked grained, poorly cemented, white to orange, quartzose sandstone. Sand grains are Sandstone 80-100 Shaly sediments. The geologic formations are thin in relation to their aerial extent and would only Os Crooked moderately- to well-rounded and well-sorted. The sandstone is structureless, and South be one-tenth as thick as shown on the cross sections if no vertical exaggeration were used. The Creek Os Opg 300 lr 350 Fork Creek less commonly, shows subtle cross stratification. The lower St. Peter Sandstone Siltstone U Creek exaggeration needed to show the thin rock formations gives the appearance of steeper slopes on D 250 River is more feldspathic and shaley, but this part of the formation is not exposed in the St. Lawrence 31 36 Ops 36 the bedrock unit contacts, the land surface, and bedrock topography. 31 31 36 31 s G Shale Ops 36 region. There is an unconformity at the basal contact with the Shakopee Formation Formation 60-70 350 With the exception of the Mt. Simon Sandstone, all of the Paleozoic units shown on this G Beaver (Smith and others, 1993). The uppermost surface is generally iron crusted and 350 M 31 Od plate can be seen at the land surface somewhere in Houston County. The sedimentary rocks G 300 burrowed. The St. Peter Sandstone is commonly exposed along hill slopes that Chert differ in their resistance to weathering and erosion, as indicated by the weathering profile on 350 Os lr WISCONSIN 6 1 are capped by the Platteville and Glenwood Formations. The maximum thickness 1 6 Winnebago 6 6 1 Reno Oolites 1 Ops 6 the lithology column of Figure 1. The units that cover the largest areas of the map are the most of the St. Peter Sandstone ranges from 70 to 90 feet (21 to 27 meters). PALEOZOIC G Clear resistant to weathering and generally form plateaus composed of carbonate rock (limestone and Lone Rock A 400 350 Creek Prairie du Chien Group lr G Glauconite 350 dolostone). The soft sandstone and shale formations are easily eroded and occur within the walls Formation 350 G 135-150 Ops Shakopee Formation (Lower Ordovician)—Tan to gray dolostone, sandy dolostone, Ph Phosphate grains Opg Creek of valleys.