Landscape Features of Iowa by Jean Cutler Prior   The topographic features shown here illustrate the range of picturesque diversity that is present across our state. In addition to their beauty, each of these landscape views reflects some aspect of Iowa’s geologic history. Understanding the geologic setting of various types of terrain is essential for citizens concerned with farming, urban expansion, recreation, excavation of mineral resources, pumping of groundwater supplies, landfilling of waste materials, and other environmental and natural resource issues. Also, it is useful to think about these landscapes in terms of their influence on the distribution of native plant and animal habitats, on various soil types, on the potential for archaeological remains, and on patterns of historic settlement. Learning more about the features of Iowa’s landscape increases our understanding and appreciation of the views around us and the ground beneath our feet.   Photo by Jean Prior. Shifting sand dunes occupy part of an abandoned channel of the Upper Iowa River in Allamakee County. The sand accumulated when water flowed through this meander much earlier in the valley’s history. Wind also deposited sand here during later dry periods. Photo by Gary Hightshoe, Iowa State University. The Iowa River forms sweeping meander loops as it flows across its floodplain in Tama County. Scars of earlier migration channels of the river are visible in the fields and woodlands. Floodplains are underlain by porous alluvial deposits that yield valuable groundwater supplies. These shallow resources are vulnerable to contamination from the land surface. Photo by Gary Hightshoe, Iowa State University. The island-braided channel of the Mississippi River occupies the floor of a gorge eroded through steep rock-lined bluffs in Clayton County. The deeply entrenched river valley was shaped by glacial meltwater floods between 18,000 and 9,500 years ago. Photo by Tim Kemmis. Hump-backed ridges rise from the gently rolling landscape in southeastern Linn County. These ridges, known as paha, are always oriented NW to SE. They are all that remain of a once higher glacial plain and are often capped with wind-blown loess and sand. Photo by Pat Lohmann. A glacial moraine in Dickinson County appears as a series of irregular broken ridges crossing the landscape. These are the hummocky accumulations of pebbly debris that settled out of stagnant, slowly melting glacial ice about 13,000 years ago. Photo by Doug Harr. Ocheyedan Mound is an isolated, conical hill composed of sand and gravel. It is an excellent example of a glacial kame, formed as meltwater carried sediments off the glacier surface and deposited them into a cavity in the slowly melting ice. Photo by Stan Mitchem. Gullies are deep, narrow erosional cuts through the landscape. Their development and growth is an active geologic process within the silt-dominated Loess Hills topography of western Iowa. Gullies widen and lengthen headward (upslope), eroding quickly, especially after heavy rains. Photo by Gary Hightshoe, Iowa State University. Crooked ridges with steep sideslopes characterize the Loess Hills of western Iowa. They are composed of thick deposits of silt carried by the wind from the adjoining Missouri River valley during seasons when glacial meltwater flood sediments were exposed. There is a sharp contrast between prairie and encroaching woodlands in this topographic setting. Photo by Don Poggensee. Some of Iowa's most fascinating scenery is found in the Loess Hills. The alternating peaks and saddles along diverging ridge crests were sculpted from thick deposits of loess, carried by wind from the adjoining broad valley of the Missouri River. The loess originated as silt, left in the valley following glacial meltwater floods between 12,000 and 50,000 years ago. Photo by Pat Lohmann. Glacial erratics are boulders of igneous and metamorphic rock, native to geographic regions well north of Iowa. The erratics in this Black Hawk County pasture were carried into Iowa by glacial advances over 500,000 years ago. They were concentrated at the land surface by later erosion, which removed the fine-grained deposits once surrounding them. Photo by Gary Hightshoe, Iowa State University. Circular depressions, some filled with water or clumps of trees, mark the location of sinkholes in this Clayton County aerial view. Sinkholes form by collapse of thin soil and unstable rock into underground crevice or cave openings. Shallow aquifers are vulnerable to contamination problems in this geologic setting. Though most common in northeastern Iowa, sinkholes are also seen in Floyd and Mitchell counties and in the Burlington area of southeastern Iowa. Photo by Gary Hightshoe, Iowa State University. These shallow wetlands are a series of glacial kettles on Doolittle Prairie State Preserve in Story County. A subtle drainage system connects them, as noted by the soil moisture and vegetation patterns. These linked “prairie potholes” mark a route taken by glacial meltwater through a maze of slowly disintegrating glacial ice about 13,000 years ago. Photo by Gary Hightshoe, Iowa State University. Dendritic drainage patterns crease these cropped fields with branching routes along which precipitation runoff is channeled into rills, creeks, and rivers. This effective drainage network has reshaped the glacial plains left after southern Iowa’s last contact with glaciers, over 500,000 years ago. Photo by Gary Hightshoe, Iowa State University. Long continuous rock bluffs, called palisades, line the Upper Iowa River valley. These picturesque cliffs result from the river eroding against dolomite, a resistant rock unit formed 450 million years ago. Such scenic landscapes in northeastern Iowa reflect the presence of sedimentary bedrock formations close to the land surface. Photo by Greg Ludvigson. This inside view of a cave entrance at Maquoketa Caves State Park illustrates an example of karst topography. Such features also include springs and sinkholes, landforms which result from groundwater movement slowly dissolving shallow limestone or dolomite bedrock. Photo by Jean Prior. An outcrop of sedimentary rock displays horizontal layering, which reflects the rock’s origins in a marine environment. Vertical fractures, caused by later earth stresses on the brittle dolomite, contribute a blocky appearance to the outcrop. These various planes of weakness are flowpaths for groundwater movement. Photo by Art Bettis. The discharge of water from Cold Water Spring crosses a series of rock riffles as it flows away from a bluff of dolomite bedrock. Springs develop where groundwater flow is intercepted by the land surface, usually along the steep sides of valleys. Photo by Pat McAdams. The oldest bedrock formation visible anywhere in Iowa outcrops at Gitchie Manitou State Preserve in Lyon County. The distinctive reddish cast of the Sioux Quartzite is seen here along the edges of "Jasper Pool," an 1800’s-era quarry on the preserve. These durable, quartz-rich rocks are 1.6 billion years old. Glacial erratics of this formation are easily recognizable and may be found for many miles to the southeast. Adapted from Iowa Geology 1995, Iowa Department of Natural Resources