Iowa Geology 2001

IOWA GEOLOGY 2001

Number 26

1 IOWA GEOLOGY 2001

Iowa Department of Natural Resources Jeffrey R. Vonk, Director

Geological Survey Bureau 109 Trowbridge Hall Iowa City, Iowa 52242-1319 (319) 335-1575 www.igsb.uiowa.edu

Donald L. Koch State Geologist and Bureau Chief

COVER

The cool moist surface of a sandstone outcrop provides favorable habitat for a lush growth of liverworts (flat plants), mosses (dark green), and ferns in Clayton County. Throughout the state, geology and ecology combine to create natural areas of great beauty and scientific interest.

Cover photo by Clay Smith

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Jean Cutler Prior Editor Patricia J. Lohmann Publication Designer

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Printed on Recycled Paper

2 This issue is dedicated to Donald L. Koch, retiring State Geologist of Iowa – for 42 years a researcher of fossils, rock strata & groundwater; advisor to well drillers, aggregate & gas- storage companies; leader of the Geological Survey & supporter of informative publications for Iowans.

The Age of Dinosaurs in Iowa 2 Monitoring Iowa’s Waters 8 Keeping Ahead of Groundwater Quality Questions 10 Baseflow: Where Groundwater Meets Surface Water 12 Topographic Relief Map of Iowa 14 The Geology of Pikes Peak State Park 16 Keokuk Water Works: Its Geological Foundations 22 Common Ground 28

1 The Age of Dinosaurs in Iowa

Brian J. Witzke

Did dinosaurs once live in Iowa? significant measure of good fortune. The simple and unqualified answer is Dinosaurs were the dominant land “Yes, without a doubt!” But the actual animals for about 170 million years of evidence for dinosaurs in Iowa is limited earth history, spanning the Late Triassic, to only a few fossils. Dinosaur fossils Jurassic, and Cretaceous periods. This have been found in several states ad- “Age of Dinosaurs” came to a close 65 joining Iowa (Nebraska, Minnesota, million years ago when a mass extinc- Missouri, South Dakota), and wander- tion ended the dinosaurs’ reign. (Almost ing dinosaurs would have been unim- all paleontologists consider birds to be peded by these artificial boundaries. descendents of small carnivorous dino- Fortuitous circumstances are saurs, so a segment of the dinosaur pedi- needed to preserve dinosaur remains in gree survived this extinction.) Sedimen- ancient sedimentary environments. Fol- tary deposits from the Age of Dinosaurs lowing the death of an animal, the cover extensive portions of Iowa and bones need to be buried within the sedi- have real potential to yield dinosaur ments and protected from chemical and fossils. The Jurassic Fort Dodge Forma- mechanical destruction. Many great tion was deposited at the same time as dinosaur discoveries are associated with strata in the American West that have sediments of ancient river systems, produced remarkable dinosaur fossils, where dinosaur bones may be preserved but no Jurassic dinosaur fossils have yet within floodplain and river channel de- been found in Iowa. The Cretaceous posits. The discovery of fossil bones is formations are more widespread in Iowa, aided by a careful understanding of a and these same formations have pro- region’s geology (where to look), consid- duced dinosaur fossils at scattered lo- erable patience (keep looking), and a calities in the central United States.

2 “Dinosaur Society Hadrosaur,” by natural history and wildlife artist Karen Carr, courtesy of www.TheFernleaf.com

Hadrosaurs, commonly known as duck-billed dinosaurs, occupied subtropical environments in the coastal lowlands of the central United States during the Cretaceous Period, about 100 million years ago.

Iowa’s oldest Cretaceous sediments, in 1928 from the Missouri River bluffs the Dakota Formation, were deposited near Decatur, Nebraska. This locality in ancient river systems that drained lies only about one mile from the Iowa westward to an interior seaway during border. Although this fragmentary fossil the middle part of the Cretaceous pe- has not been assigned to a particular riod, about 95 to 100 million years ago, dinosaur species, its features are suffi- a time of global “greenhouse” warming. cient to identify it as a large ornithopod, Floodplains and coastal lowlands were a highly successful group of generally covered with lush subtropical vegetation bipedal plant-eating dinosaurs. The pro- at that time, providing suitable habitats portions of this leg bone, when com- for dinosaurs. The first dinosaur fossil pared with other ornithopods, indicate a found in the Dakota Formation, a por- dinosaur that was about 32 feet long. tion of a leg bone (femur), was collected This Dakota fossil likely represents an

3 The microscopic structure of a petrified dinosaur bone fragment from Guthrie County, Iowa, shows a once-porous network of vascular canals for blood vessels. (Enlarged 3-mm-wide view.) Brian Witzke

early hadrosaur. Hadrosaurs are a well- cient river gravels of the Dakota Forma- known family of “duck-billed” ornith- tion in Guthrie County. The micro- opod dinosaurs that comprise the most scopic structure of this fragment (shown abundant and diverse group of Late above) revealed densely vascularized Cretaceous dinosaurs in North America. bone, indistinguishable from that seen Other dinosaur fossils have been in typical dinosaur bone. Although not uncovered from the Dakota Formation terribly impressive by itself, the Guthrie in nearby northern Kansas, eastern Ne- County discovery confirms that dinosaur braska, and Minnesota. A family of fossils indeed occur in the Dakota For- heavily armored ankylosaurian dino- mation of Iowa. saurs, the nodosaurids, is represented by The river deposits of the Dakota partial skeletons of a ten-foot-long crea- Formation were progressively flooded by ture known as Silvisaurus. Additional marine waters as a vast interior seaway hadrosaur bones have been found in encroached eastward later in the Creta- Minnesota. Three-toed fossil footprints ceous, and a succession of younger shale of ornithopod dinosaurs have been dis- and chalk deposits were laid down on covered recently in Dakota strata. the ancient sea bottom in western Iowa. In Iowa, a fragment of fossil bone These strata, named the Graneros, was found by the author in 1982 in an- Greenhorn, Carlile, and Niobrara for-

4 Dinosaur-bearing Cretaceous strata in Iowa and adjoining states

Æ MN Dickinson Co. Æ

SD Æ Plymouth Co. WS IL

Decatur, NE Æ

Guthrie Co. Æ

MO

Æ NE 050100miles KS

Tertiary Cretaceous Precambrian Ogallala sand and silt Dakota sandstones and shales quartzites and igneous rocks Cretaceous Paleozoic Location of known marine shales and chalks undifferentiated dinosaur fossils

mations, have yielded bones of large times linked with dinosaurs in the marine reptiles known as plesiosaurs public’s imagination, plesiosaurs actually from several localities in Iowa. In nearby represent an unrelated group of extinct areas, these same formations have also marine reptiles. Long- and short-necked produced fossils of other extinct reptile plesiosaurs plied the waters of the Cre- groups including mosasaurs (giant sea taceous interior seaway with large lizards) and pterosaurs (large flying rep- paddle-like flippers in search of fish and tiles). Although plesiosaurs are some- other prey. The marine shales and

5 Fossil bone from the Dakota Formation in the Iowa area indicates that large ornithopod dinosaurs once inhabited the region. Reaching a length of 32 feet, these plant-eating giants browsed the lush subtropical forests and swamps. (Six-foot-tall human for scale.)

chalks of this seaway also yield the re- derived from erosion of the Cretaceous mains of true dinosaurs. Dinosaurs cer- strata that underlie large areas of the tainly did not live at sea, but occasion- northern Great Plains. Reworked and ally a carcass would float out to sea, transported Cretaceous fossils, such as decay, and settle to the bottom. The plesiosaur bones and shark teeth, are discovery of dinosaur bones and teeth sometimes found in the glacial tills and (of hadrosaurs and ankylosaurs) in ma- associated gravel deposits in Iowa, espe- rine strata from nearby Minnesota, cially in the western part of the state. South Dakota, and Kansas certainly Two dinosaur bones can now be added raises the possibility of similar discover- to the list of Cretaceous fossils recov- ies in western Iowa. ered from glacially derived gravels in Long after extinction of the dino- Iowa, and to date these discoveries rep- saurs, huge continental glaciers ad- resent the best dinosaur fossils found in vanced and retreated across Iowa during the state. the “Ice Age” (the last 2.5 million Charlie Gillette of Dickinson years). These advancing glaciers incor- County picked up a dark-colored, 3-inch porated large volumes of rock and other fossil bone from a load of landscaping sediments as they moved across the con- gravel that came from a nearby gravel tinent. Much of the glacial material was pit. When his uncle Jack Neuzil, a re-

6 Fossil dinosaur vertebrae 3 and 4 inches long have been found in Dickinson (right) and Plymouth (far right) counties, Iowa, respectively. These specimens likely came from hadrosaurs. photos by Paul photos VanDorpe by Paul

tired educator and dinosaur enthusiast, 1930s he picked up a fossil bone from a saw the bone he suspected that it could conveyer in a gravel pit near Akron in be a dinosaur vertebra. His suspicions Plymouth County, and the bone was were confirmed by a leading dinosaur kept on a shelf and occasionally used as paleontologist, and the discovery of a doorstop in the family’s home. In re- Iowa’s first identifiable dinosaur bone sponse to a recent newspaper article was soon reported in the Des Moines about dinosaurs in Iowa, Mrs. Register (9/7/2000). The fossil is a tail Michaelson contacted the Geological vertebra from an unknown dinosaur, Survey Bureau and brought the bone in possibly a hadrosaur. for identification. It is a partially weath- Following this discovery, a second ered 4-inch dinosaur vertebra, likely dinosaur vertebra from Iowa has come from an hadrosaur. to light thanks to Doris Michaelson of It’s only a matter of time before Bellevue. Her father, John Holdefer, had some lucky searcher examining Iowa’s a keen eye and was fascinated by the Cretaceous formations or Ice-Age grav- rocks and fossils that he saw as a Mate- els finds the next dinosaur fossil from rials Inspector for the Iowa Highway Iowa. So keep looking! ❖ Commission. Sometime in the mid-

7 Monitoring Iowa's Waters

Bernard E. Hoyer photos by Ken Formanek

We require water for life, share its tation. The program focuses on ambient ownership and stewardship, benefit from water conditions. This means that all its use for business and recreation, and, types of water resources are being in order to manage it, we need water looked at across the state to gain a fair quality data. The mission of the Iowa and consistent appraisal of their condi- Water Monitoring Program is to con- tion. It is not concerned just with duct an ongoing assessment of the con- known water quality problems, or with dition of the state’s surface water and checking on regulatory compliance – groundwater resources and to report aspects of monitoring that have existed results so that appropriate information is for years. It is “big picture” monitoring, available to guide resource management and it can lead to many practical poli- policies and decisions. cies and management decisions. This The program requires collection of program is growing and adapting with reliable, objective statewide data on a the strong emphasis placed on it by the continuing basis and delivery of infor- Governor, the General Assembly, and a mation through various means. Key diverse coalition of other groups. goals are a scientific description of wa- Initial emphasis has been placed on ters, measurement of changes in quality, improved monitoring of Iowa’s interior identification of trends, delivery of infor- rivers and lakes and developing a data mation to the public, and public in- management system that can capture volvement with their water resources. data effectively and deliver it to govern- The uniqueness of this monitoring ment and public users. program lies in its comprehensive na- Data collection is the most impor- ture, including rivers, lakes, wetlands, tant and expensive portion of the pro- and their ecological communities; gram. Iowa’s interior rivers and streams groundwater from the water table to plus 132 lakes are monitored for over deep bedrock aquifers; and even precipi- 200 chemical, physical, and biological

8 Left: Identifying small invertebrates found in streambeds provides an indicator parameters, including pesticides, phar- of water quality. maceuticals, and volatile organic com- pounds. All state-owned beaches are monitored for indicator bacteria groups throughout the swimming season. Groundwater is monitored from avail- able public, private, and specially in- stalled monitoring wells. All field and Right: This device laboratory methods and techniques are measures such water recorded to insure future comparability characteristics as pH, of data for scientific analysis. dissolved oxygen, and Following the sampling phase, data turbidity. management, coordination, and inter- pretation are crucial areas of the pro- gram, as well as the production of re- ports for management purposes and for the public. Other agencies will be en- couraged to add their data to a central clearinghouse to ensure long-term curation and widespread availability. Timely interpretation, annual as well as Above: Following electro-shocking, long-term, is essential as monitoring fish can be counted, identified, and data accumulates through the years. examined before being released. Finally, keeping Iowans informed is vital to the success of this monitoring program. Resource managers, elected Monitoring Iowa’s waters is a long- officials, special interest groups, and the term investment. The program must public need to be aware of what is done continue uninterrupted, without gaps in and learned. Part of this citizen involve- data, to attain its goals and maximize its ment includes the IOWATER program, usefulness to Iowa. At the same time, targeted at educating the public by the program must maintain flexibility training volunteers to monitor water and adjust as experience is gained and resources in their home areas. technology improves. ❖

9 Keeping Ahead of Groundwater Quality Questions

Robert D. Libra photos by Dave Conell (USGS)

For almost two decades, the Geologi- and synthetic organic chemicals added to cal Survey Bureau, in partnership with the the analyses. Environmental parameters U.S. Geological Survey (USGS) and the such as organic carbon and dissolved oxy- University Hygienic Laboratory, has moni- gen also joined the list. The number of tored the quality of raw untreated ground- wells sampled increased for a time to over water from individual municipal wells. 200 per year, but decreased to the 45 to The size of this effort has varied through 90 range in the late 1990s. time, with available state and federal fund- Results from this cooperative moni- ing. Focus of the monitoring has evolved toring network are a key part of our knowl- as well, in response to changes in society’s edge about the state’s groundwater qual- questions about the quality of our ground- ity. They allow for prediction of natural water. and contaminant-related water quality of In the early 1980s, between 150 and our major aquifers, and thus let us know 200 wells were sampled annually and ana- whether their quality will support various lyzed primarily for “natural” constituents. uses. Is the water too hard for a boiler, or These included minerals such as calcium, does it have too much sulfate for supply- magnesium, bicarbonate, sulfate, iron, and ing a dairy? Would we need to purge the manganese; the more common nutrients iron and hydrogen sulfide to make it pal- such as nitrate; and radioactive com- atable? Will the water meet public drink- pounds such as radium. As various ing water standards? Will the quality pose groundwater investigations began to show odor problems if used with an anaerobic the presence of agricultural and other con- lagoon? taminants in “vulnerable” aquifers, the Many such questions are known to program emphasis shifted towards shallow the water supply industry. However, new aquifers, with more nutrients, pesticides, questions always arise, and one of the most

10 Emmetsburg Municipal Well #4 is 35 feet deep and taps gravel deposits along the Des Moines River valley. The well has been sampled periodically as part of a long-standing cooperative program with the U.S. Geological Survey.

important uses of groundwater monitor- ing information is to supply answers for high enough concentrations in some questions that haven’t been asked before. groundwaters to cause treatment prob- For example, nitrogen in the form of lems. This occurs fairly commonly, and ammonia may undergo troublesome reac- predictably more so in some aquifers than tions during some types of water treat- others. There is no contaminant source ment, and even have a negative effect on to search for. the treatment process itself. In the past, Other such questions are being raised. water supply wells were rarely analyzed for Researchers are coming to realize that ammonia, based on the “conventional relatively low concentrations of phospho- wisdom” that ammonia doesn’t occur in rus impact stream and lake environments, significant amounts in groundwater, un- so we need to assess the natural back- less it is grossly polluted. When a water ground levels in groundwater feeding supply did show measurable ammonia, the streams and lakes. Also, there has been a search was on for the contamination long discussion about lowering the drink- source. The usual suspects, such as nearby ing water standard for arsenic. What septic systems, leaking sewer lines, or live- would be the impact on Iowa water sup- stock manure, would be rounded up, ex- pliers if this happens? Beyond answering amined, and typically found innocent. the questions we know about, we need to Information from the groundwater moni- continue keeping our monitoring efforts toring was used to explain the situation. a step ahead – collecting answers before Ammonia does indeed occur naturally in the questions are asked. ❖

11 Baseflow WHERE GROUNDWATER MEETS SURFACE WATER

Keith E. Schilling photo by J.R. Olson

It's late summer and it hasn’t rained to wet or dry weather. During extended in a month. The lawn has turned brown dry periods, the water table falls below and farm fields are dry and cracking. Yet the streambed. Only after rainfall has a trip down to the nearby stream chan- replenished the groundwater supply nel finds flowing water. What you are does the water table rise sufficiently to witnessing is the interplay between intersect the streambed and resume groundwater and surface water. Ground- baseflow discharge. water seepage into a stream channel is The amount of baseflow a stream called baseflow. During most of the year, receives is closely linked to the perme- stream flow is composed of both ground- ability of rock or soil in the watershed. water discharge and land surface runoff. For example, the Floyd River in north- When groundwater provides the entire west Iowa flows through a watershed flow of a stream, baseflow conditions are composed of clayey glacial till and silty said to exist. loess. Based on a 12-year record of Groundwater discharges into stream gaging (1987-1999), each square streams when the water table (top of mile of land in its watershed produced groundwater saturation) rises above the an average of 3.7 inches of baseflow streambed. Perennial streams flow be- discharge. On the other hand, the Up- cause groundwater remains above the per Iowa River in northeast Iowa, flow- streambed throughout the year. You may ing through a watershed consisting of notice some streams flow only part of fractured limestone and dolomite, had the year, generally from spring to mid- more than twice the baseflow discharge summer, or only during wet periods. (8.0 inches per square mile). These intermittent streams occur when Baseflow is an important consider- the water table rises above or falls below ation when evaluating the health of a the base of a stream channel in response stream. Arguably, the most important

12 Streams continue to flow during extended dry periods because of contributions from groundwater. Such baseflow conditions affect water temperature, aquatic life, and delivery of pollutants to streams.

factor regarding the fate of aquatic or- primarily through groundwater dis- ganisms in surface water is the amount charge as baseflow or tile drainage (a of sustainable flow in the channel. type of modified baseflow). Point-source Streams with adequate baseflow can impacts are especially noticeable when a sustain fish and tiny aquatic organisms stream's flow consists nearly entirely of during prolonged dry periods. Since baseflow (see photo above). groundwater temperatures are nearly Ultimately it is the relationship be- uniform year-round, groundwater dis- tween surface water and groundwater charge also provides a measure of tem- during baseflow periods that may help perature stability in surface water. solve some of Iowa’s water quality issues. Streams in northeast Iowa, home to Monitoring surface water quality when several indigenous trout species, owe flow consists entirely of baseflow can be their temperate conditions to contribu- used to identify and locate sources of tions from baseflow and spring dis- pollution. In turn, these pollution charge. However, in some cases, dis- sources can be addressed at their origin charge of pollutants in baseflow may so that baseflow water quality improves have detrimental effects on surface wa- over time. We can all understand the ter quality. Nitrate-nitrogen, a common need for quality baseflow in our streams, pollutant in Iowa’s streams, is delivered especially during a hot Iowa summer. ❖

13 Topographic Relief Map of Iowa

James D. Giglierano Jean C. Prior

This soaring view of Iowa’s terrain shows the unevenness, or relief, of the land surface. Particularly noticeable are the large number of rivers within the state and the directions in which they flow. Using river alignments, can you follow the Missouri-Mississippi drainage divide along its length in Iowa? The amount of topographic relief and the patterns of stream dissection are related to underlying geologic materials. In northeastern Iowa, sedimentary bed- rock at the land surface sharpens and steepens the landforms. In far western Iowa, adjacent to the level Missouri River valley, rise the intricate blufflands of the silt-dominated Loess Hills. Fresh glacial drift deposited just 14,000 to 12,000 years ago across north-central Iowa yields level terrain, only a few well- developed rivers, and a landscape scored with curved ridges of glacial moraines. years old), and extensive erosional In contrast, drainage networks are well sculpture is evident. established across the much older glacial This computer-generated map is deposits of southern Iowa (over 500,000 based on a grid of land surface eleva-

14 tions artificially illuminated from the These clearly demonstrate remarkable northwest. The intriguing view reveals a differences in Iowa’s terrain from one variety of physical shapes and features, part of the state to another. ❖ as well as broader landscape patterns.

15 THE GEOLOGY OF Pikes Peak State Park

Brian Witzke and Ray Anderson photos by Clay Smith

The northeast Iowa area around McGregor's Landing was located at the Pikes Peak State Park in Clayton site of the town that now bears his County is one of the most beautiful and name. The Pikes Peak area was owned interesting regions of Iowa. Its precipi- by McGregor, and, as a favorite family tous rock bluffs record a geologic history picnic spot, it was protected from being beginning over 500 million years ago. logged for firewood to feed the hungry Various plant and animal communities have inhabited the region, shifting and evolving with climatic and cultural changes. The long history of its Native American residents is symbolized by the large number of mounds along ridge tops, many shaped as animal effigies. The arrival of Father Marquette and Louis Joliet in the region in 1673 opened a rich, new phase of regional history. French hunters, trappers, and miners were among the early historic residents. The region became a part of the United States with the purchase of the Louisiana territory in 1803, and was explored by Zebulon Pike shortly there- after. Military forts were built, towns established, and roads constructed. In 1837, Alexander McGregor established a ferry across the Mississippi River.

16 riverboat boilers. Owner- ship of the area passed down through McGregor’s relatives, until it was given as a gift to the federal gov- ernment. The property was later conveyed by Congress to the State of Iowa and became Pikes Peak and Point Ann state parks in 1935. Since settlers had never been allowed on the land, Pikes Peak today probably appears much as it did hundreds of years ago. An instructive and picturesque succession of geologic strata is wonder- fully displayed within Pikes Peak State Park. The down- cutting of the Mississippi River valley has exposed a number of geologic forma- tions in bold cliffs and steep ravines. Above: The highest bluffs at Pikes Peak are The oldest rock formation exposed in underlain by massive Paleozoic-age dolomites of the area is the Jordan Sandstone, which the Galena Group. They provide panoramic views of the Mississippi River valley and its outcrops at Point Ann at the north end confluence with the Wisconsin River – the spot of the park. The sandstone, about 100 where French explorers Marquette and Joliet feet thick, was deposited during the first saw the Upper Mississippi Valley in 1673. latter part of the Cambrian Period, about 505 million years ago, as beach Far left: Water splashes over Bridal Veil Falls, a and near-shore sands of a slowly ad- resistant ledge of 460-million-year-old dolomite vancing and retreating sea. The Jordan of the Platteville Formation (Ordovician).

17 Sedimentary bedrock outcrops form bold bluffs throughout Pikes Peak. These rock strata vary in their resistance to weathering and erosion. The result can be rough-textured ledges over- hanging smooth-textured recesses. (Prairie du Chien dolomite shown here.)

per Mississippi Valley to the Twin Cities. The dolomite layers were originally de- posited as lime sediments in a shallow tropical sea that covered much of the interior of North America between about 490 and 505 million years ago. These sediments were subjected to later chemical replacement by dolomite. The Prairie du Chien seas eventu- ally withdrew from the interior of North America during later stages of the Early and Middle Ordovician, beginning a Sandstone is an important aquifer, pro- remarkably long period of erosion that viding water to wells across much of continued for 25 million years. This eastern Iowa, including wells for drink- erosional period was characterized by ing water at Pikes Peak. extensive weathering of the landscape, Above the Jordan Sandstone is the the cutting of deep river valleys, and the Ordovician-age Prairie du Chien Group, production of a network of caves and named for the nearby city of Prairie du sinkholes, known to penetrate up to 350 Chien, Wisconsin. These strata include feet deep in areas of eastern Iowa. As a succession of dolomites with minor the seas again returned to the area, the sandstone and shale, which reaches deep valleys were filled with sand and thicknesses up to 220 feet in the park. shale, and a remarkably homogeneous The erosionally resistant dolomite forms interval of fine quartz sandstone was bluffs, exposed at Prairie du Chien and deposited across the region. This upper northward throughout much of the Up- blanket of sandstone and the underlying

18 valley-fill succession of variably colored sandstone and shale comprise the St. Peter Sandstone. The lower unit is of special interest in the area of Sand Cave in the park, where iron staining has pro- duced rich colors, with reds, oranges, browns, and purples coursing through a mostly buff- to white-colored matrix of quartz sand (see p. 21). Directly above the St. Peter Sand- stone, lies the gray-green Glenwood Shale. Only about four to five feet thick in the park, the shale is soft and easily erodible, so it is typically not well ex- posed in the park’s wooded ravines. The clay sediments that formed the Glenwood Shale were deposited very Prairie du Chien dolomite forms broad-shouldered slowly in a shallow seaway, probably far outcrops on hillslopes from shore. (above), and tiny grottos The Platteville Formation, a 45- within its weathered surface (inset right). In contrast, water wears the St. Peter Sandstone into smoothly contoured slopes (left).

foot-thick succession of limestone and dolomite strata, is exposed in the upper slopes in Pikes Peak State Park. It repre- sents lithified sediments deposited in a broad tropical sea, which supported a diversity of shelled bottom-dwelling

19 animals. The unit can be most easily valley southward to the Dubuque area. viewed along the park’s boardwalk, The modern Pikes Peak State Park where a small creek cascades over a landscape, dominated by steep bluffs, is resistant dolomite ledge to create Bridal the product of dramatic sculpting of the Veil Falls. bedrock strata and deep incision by the The uppermost rock interval ex- Mississippi River. The floor of the Mis- posed at Pikes Peak is the Galena sissippi bedrock channel lies some 300 Group, composed of the basal Decorah feet below the modern river level. This and the overlying Dunleith formations. deeper level of down-cutting was likely The Decorah Formation is a succession related to episodes of continental glacia- of shale and limestone. The shales, typi- tion during the last 2.5 million years, cally greenish-gray in color, include when vast ice sheets were present in the spectacular lenses of brachiopod fossils. Northern Hemisphere, lowering global Interestingly, these shales also include sea level up to 400 feet, and increasing thin but widespread layers of altered the gradient of the Mississippi River. volcanic ash derived from distant erup- Then, as the ice sheets began to melt, tions near present-day Virginia. The huge volumes of meltwater and sedi- clay shales and embedded ash deposits ment moved down the Mississippi Valley are soft and easily weathered, so they and other drainageways scouring and are not well exposed in the park. deepening the valley. As sea levels pro- Above the Decorah, however, the gressively rose once again, the sediment- massive Dunleith Formation forms the laden meltwaters deposited large vol- highest cliffs and ledges within the park. umes of sand and gravel within the val- These resistant dolomite and limestone ley. beds are well displayed at the main Mis- Pikes Peak State Park, perched high sissippi River scenic overlook and in old on the bluffs overlooking the Mississippi quarry workings within the park. The River in Clayton County offers an irre- Dunleith contains almost no shale and sistible combination of natural beauty, is dominated by dolomite, which dis- colorful history, and informative geo- plays a considerable quantity of nodular logic exposures. It rates as one of Iowa’s chert (“flint”). This formation reaches greatest natural treasures. ❖ thicknesses of 80 feet in the park and forms cliffs along the Mississippi River

20 from SANDSTONE to SAND PAINTINGS

Well-rounded grains of nearly pure quartz sand compose the St. Pe- ter Sandstone. This formation is up to 200 ft thick in the Pikes Peak region, and its massive beds stand out among the bluffs and steep-walled ravines. Of special interest in its lower portion are dramatic reddish-orange swirls and bands of iron-oxide cements (photo, right). These colors were imparted by mineralized groundwater moving through the porous sandstone. Captivated by the array of colors at Pictured Rocks or Sand Cave, as into drug jars, color by color, upside the site is known, Andrew Clemens, down through their narrow openings. an 1880s resident of McGregor, cre- Completed artworks were sealed with ated exquisite, three-dimensional sand wax and inverted. Shown left are two paintings in bottles. During his 20s sides of one jar, with George Washing- and 30s, he created intricate designs ton astride a white horse on one side, and pictures by layering loose sand and two Native Americans, the State Seal of Iowa (including motto), and a steamboat on the other. Note Clemens’ signature in the red sand below the boat.

Adapted from: Wagasky, Rashelle, 1997. One in a Million. Iowa Heritage Illustrated, State Historical Society of Iowa, Spring, 1997, p. 48-49. Also, Anderson, R.R. and Bunker, B.J. (eds). 2000. The Natural History of Pikes Peak State Park, Clayton County, Iowa. Geological Society of Iowa, Guidebook 70, Nov. 2000, 139 p.

Photo above by Ray Anderson.

Photo left courtesy of State Historical Society of Iowa – Des Moines. Photographer: Chuck Greiner.

21 Keokuk Water Works ITS GEOLOGICAL FOUNDATIONS

Jean C. Prior and Robert M. McKay photos by Paul VanDorpe and Robert M. McKay

There is often more than meets the Congress ordered a survey of the rapids, eye in a municipal water supply. This is which was entrusted to Captain especially true of the city of Keokuk, R[obert] E. Lee of the corps of engi- Iowa, and its water works. Sandwiched neers (and later Civil War General). By between the Mississippi River’s flow on his estimate, the length of the rapids is one side and 345 million-year-old lime- eleven miles, with a fall of twenty-four stone bluffs on the other, the city’s feet. Here the Mississippi tumbles over state-of-the-art water plant is expanding ledges of blue limestone which are at all and is literally anchored to its geological times more or less covered with water foundations. With its special geologic and through which many crooked chan- setting and the city’s interest in educat- nels have been worn.” * ing the community about its drinking These exposures of resistant bed- water supply, Keokuk’s Municipal Water rock are assigned to the Mississippian Works has put out the welcome mat for Subsystem, one of the basic divisions of visitors to tour this fascinating facility. geologic time recognized throughout the This Iowa stretch of the Mississippi world. In fact, Mississippian-age strata River has attracted geological interest were so-named in the geologic literature for well over 150 years. The final sweep- of the late 1800s for this Iowa segment ing curves in the state’s eastern border of the Mississippi River valley. To geolo- between Burlington and Keokuk are gists, these rock outcrops are the start- formed by bluffs of massive limestone, ing point for the definition of strata of and the rapids at Keokuk were a noted this age. obstacle to early exploration and travel The lime-rich sedimentary rocks by river. J.N. Nicollet writes, “In 1838 actually had their origins 345 million

22 Keokuk Water Works, barely visible beyond Lock and Dam #19 on the far shore, is dwarfed by the broad expanse of the Mississippi River. Its width was scoured by the erosive action of glacial meltwa- ters that periodically flooded the valley over 9,000 years ago. Sweeping curves along the valley are defined by limestone bluffs of Mississippian age, a term of geologic time recognized worldwide and named for this segment of the Mississippi Valley between Keokuk and Burlington.

years ago in shallow tropical seas that nating with south-bound glaciers that submerged the continent’s interior, in- periodically gripped the midcontinent in cluding Iowa. The rocks bear fossil re- sub-Arctic cold between 2.5 million and mains of abundant marine organisms 10,000 years ago. Bedrock promontories, that inhabited these warm seas, an envi- such as here at Keokuk, were left stand- ronment resembling the clear waters of ing as the river gradually deepened its the Florida Keys today. Lime sediments valley, especially during the later chap- were precipitated from seawater and ters of the state’s Ice Age history. Epi- also were produced biologically as ani- sodes of glacial melting, especially be- mals such as corals, crinoids, brachio- tween about 100,000 and 9,000 years pods, and snails built their skeletal shel- ago, sent meltwater floods surging down ters. the Mississippi, scouring the valley floor The Mississippi River itself ap- still deeper, and then partially back- peared much later in time, likely origi- filling the gorge with thick deposits of

23 sand and gravel. right outside the Keokuk Water Works, The most significant event in the and its operation and river traffic add river’s modern history has been con- considerable interest to visitors. struction and maintenance of a nine- But the story is not complete. In foot navigation channel and its accom- 1877, citizen William Stripe’s concern panying lock and dam system built to for safe drinking water led him to found facilitate commerce throughout the a private company known as the Keokuk region. Lock and Dam #19 is situated Waterworks. Its purpose was to gather

24 Mississippi River water is entirely new treatment plant was begun pumped through a net- as a phased replacement of the older work of pipes into massive facilities. cone-shaped clarifiers The first important issue was loca- where sediment and dis- tion. The site on the Mississippi River solved minerals are re- moved from the swirling still looked good over 100 years later water. Keokuk’s expanded, because it already had functioning river- state-of-the-art water intake pipes and underground settling plant includes a 12-ft-high tanks that could be converted to clean portion of the 345 million- water storage. In order to construct the year-old Mississippian new building on top of the 1979 settling limestone bluff along one entire interior wall of the tanks, engineers designed a pillar an- 300-ft-long building. chored into underlying bedrock to sup- port the weight of a new 1.3 million- pound re-carbonation unit. Construction at the existing site also entailed excavating into the steep bedrock bluff to create more space. Contractors removed about 200,000 cubic feet of rock and cut a stair-step into the bluff so that massive cone- shaped water clarifiers and softeners would have a solid foundation. Phase I of the new facility is complete, and in- cludes a 14 million-gallon-per-day treat- and treat Mississippi River waters for ment process. With an eye to future distribution to citizens and industries of expansion, the pipes and space are in the prospering city. In 1938 the com- place to add new filters and more clari- pany was purchased by the City of fying and softening cones as needed. Keokuk, and a new treatment building Excavation into the valley bluff was constructed, with further improve- exposed two of the local Mississippian ments in subsequent decades. Then, in bedrock formations, the upper part of 1995, on the same piece of ground, an the Keokuk Limestone and the lower

25 portion of the overlying Warsaw Forma- tion are present behind the building. tion, a more shaley interval. Both rock Today’s Keokuk Water Works is units, particularly the Warsaw, are situated against a bluff of limestone sig- widely known for the spectacular crys- nificant in the history of the country’s tal-lined geodes that are embedded in geological investigations, a bluff of sedi- the clayey dolomite. mentary rock detailing a 345-million- Though geodes are known from year-old history of ancient seas and their many localities around the world, one of inhabitants. It overlooks a younger val- the most famous collecting regions oc- ley that was host to torrents of glacial curs within a 35-mile radius of Keokuk. meltwater floods several thousand years Rock collectors commonly refer to these ago, and whose modern descendant, the specimens as “Keokuk geodes,” and in Mississippi River, flows past the front 1967 the Iowa General Assembly de- door, providing Keokuk and its residents clared the geode as the official “State with their drinking water supply. Rock.” These roughly spherical masses The Keokuk Municipal Water of silica-rich minerals separate easily Works recognizes its unique geography from their host rock. The most prized and geology. They have incorporated specimens have hollow interiors lined the bedrock, the bluffs, the valley, the with pointed crystals of quartz and other river, and the lock and dam into their minerals. They can range in size from plant design. Inside the plant, the an- that of a walnut to a basketball. cient geode-laced Mississippian strata The geode-laden rock bluff was so form a striking visual counterpoint to interesting that it was decided to incor- the modern array of piping, tanks, porate a portion of the bluff into the valves, massive cones, catwalks, and water plant’s long west wall. About 9 computerized operations that organize feet of geode-bearing dolomite is well and treat the river’s water into a exposed along the driveway outside the municipality’s water supply (see photo new plant (see photo, p. 27), and the p. 24). rock wall then continues some 300 feet Keokuk Water Works encourages along the entire length of the building’s public tours of their plant. They know interior where the wall stands 12 feet these visits can increase the public’s high (see photo, p. 24). Smaller, less understanding not only of their local accessible exposures of Warsaw Forma- drinking water supply and its quality but

26 Layers of geode-bearing clayey dolomite, examined above by geologist Robert McKay, add great visual and educational interest to the Keokuk Water Works, both inside and outside the plant. The geodes, Iowa’s official “State Rock,” are lined with quartz (chalcedony, upper left) and calcite on quartz (lower right).

awareness of broader regional and state * Lewis, Henry. 1967 (originally published in Ger- man in 1854). The Valley of the Mississippi Illustrated. water supply issues as well. In this scenic Minnesota Historical Society, p. 219. Quote from setting, that awareness includes a J.N. Nicollet’s 1843 Report Intended to Illustrate a Map of the Hydrographical Basin of the Upper Mississippi unique reminder that we depend on and River. 26th Congress, 2nd session. Senate Docu- interact daily with geological resources ments, no. 237 – serial 380, p. 24, 26. and geological processes past and present. ❖

27 COMMON GROUND

In the field of ecology, the base upon which an organism lives is called its substrate. Geology is about substrates, and includes earth ma- terials that support plant and animal communities. These two fields are literally knit together by their common ground.

Examples include Pikes Peak where bedrock substrates provide ex- quisite microhabitats (see cover) as well as expansive rock-bound blufflands. In other substrate settings, Iowa’s Water Monitoring Program counts on tiny creatures that cling to the bottom of rocks in streambeds to tip off investigators about stream health and water quality. The per- meability of rock and soil substrates affects the groundwater contri- bution to a stream’s baseflow and to cool water essential for some aquatic life. Dinosaur fossils bring the dimension of time to life’s sub- strates, providing insight into the ecology of prehistoric environments. In the photo at right, a gravel substrate hosts a shoot of heat-generating skunk cabbage as it emerges through the last icy coatings of winter.

Throughout Iowa, the base upon which all life exists – our geologi- cal substrates and deeper geological infrastructure – consists of silty glacial clays, wind-blown silt and sand, river gravel and sand, as well as limestone, dolomite, sandstone, and shale bedrock. These underlying foundations affect our state’s agricultural productivity. Their engineer- ing characteristics affect building construction, and their value as min- eral and aggregate resources affects our economy. Their porosity affects both how well we contain waste buried in the ground, and at the same time how well we protect the quality of our drinking water supplies – the quality of Iowa’s human ecology.

Jean Cutler Prior Editor

2828 Clay Smith Clay Hanging Bog State Preserve, Linn County.

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