Effigy Mounds Historic Resource Study

Environment

Effigy Mounds National Monument is located in Allamakee and Clayton counties in the northeastern corner of Iowa, along the west bank of the Mississippi River. Steep bluffs, floodplain terraces, and swift cutting streams channeling deep into the bedrock terrain characterize the 2,526-acre monument. In the 1890s, Iowa State Geologist Samuel Calvin described the landscape as "gashed and furrowed in every direction by an intricate system of ramifying channels." [2] The area features a unique topography, where western prairies merge with eastern woodlands. This ecological transition zone provides one of the most biologically and topographically diverse regions in the state—a crucial factor in the success of prehistoric settlement and the development of a distinctive Effigy Mounds culture. Many of the more than 200 mounds within the monument are located on low-lying floodplains, at an elevation of 600 feet above sea level. Some mounds are situated atop the steep bluffs and open fields of the upland areas that reach, in their highest places, 1,000 feet or more above sea level.

Effigy Mounds National Monument is located on the southwestern fringe of the rugged physiographic region called the Paleozoic Plateau, which extends along the steep bluffline of the Mississippi River in Iowa and continues into Wisconsin and Minnesota. Formerly called the Driftless Area, patchy remnants of Pre-Illinoian glacial drift more than 500,000 years old recently have been discovered in the area. Unlike the rest of Iowa, the Paleozoic Plateau was bypassed by the last of the Pleistocene glaciers (the Wisconsin), allowing the region's fast cutting streams to expose and carve out deep channels in the bedrock-dominated terrain. The area is characterized by thin loess soil cover, isolated patches of glacial drift, deeply entrenched river valleys, and karst (sinkholes, caves, and springs) topography. [3]

View from Fire Point. Courtesy of National Park Service

The erosion and weakening of the shallow sedimentary bedrock of the region—primarily limestone, dolomite, sandstone, and shale—has had the greatest effect on landscape formation. Vertical cracks extending through bedrock weaken the fracture planes and create blocky rock features called joints, and the lime-rich strata slowly dissolves and enlarges cracks, crevices, and other zones of weakness to create caves and sinkholes. The catastrophic floods resulting from the melting of the last of the Pleistocene glaciers significantly altered the landscape. Alluvial flood deposits along the Mississippi River also have played a prominent role in landscape formation, creating elevated alluvial terraces such as the landform at Prairie du Chien. [4]

Recent pollen analysis studies in northeast Iowa show that spruce forests were replaced by deciduous forests before 9,100 years ago, which, in turn, were replaced by tallgrass prairie between 5,400 and 3,500 years ago and burr oak savanna about 3,500 years ago. The transition from gently rolling western prairies to the rugged, erosional terrain of the eastern woodlands that characterizes the Paleozoic Plateau creates a mosaic of micro-environmental zones in the region. Small remnant tallgrass prairies (also called goat prairies), burr oak savanna, steep-sided timber-covered valleys, towering bluffs, wetlands, swamps, and backwaters allow a wide variety of wildlife and vegetation to flourish. [5]

In August 1956, Wayne Scholtes, a soil scientist from Iowa State University, conducted soil tests on six mounds in northeast Iowa. By analyzing pollen grains found in the soil samples, Scholtes gathered information on past climate and vegetation patterns. Roger Parsons continued the soil studies in 1960 for Iowa State University, collecting seven soil profiles from mounds in and around the monument. Scholtes and Parsons' soil studies indicated that a forest environment existed on the bluffs throughout the mound-building period. Most ecologists today believe oak savanna has occupied the bluffs for the past 2,000 years. [6]

Since the first European settlers arrived in Iowa about 160 years ago, Iowa's native habitats have been greatly reduced by domestic farming, transportation- related construction projects (including railroad logging), damming of rivers for barge navigation, and draining of wetlands (especially after the Federal Swamp Land Act of 1850). James Dinsmore estimates that about 0.12 percent of Iowa's original tallgrass prairie, 4 percent of its forests, and less than 10 percent of its wetlands survived in the mid-1990s. [7] This rapid alteration of the region's environment has had drastic effects on the state's wildlife, greatly reducing the numbers of many species and extirpating others.

In their early exploration of the region, Jacques Marquette and Louis Joliet noted the proliferation of bison and deer along the Mississippi. Other mammals of pre-settlement Iowa included wolves, bobcats, mountain lions, and black bear. In the nineteenth century, historian W.E. Alexander described the abundance of wildlife in the region, including opossum, fox, owls, rabbits, eagles, woodpeckers, and cuckoos. Ellison Orr observed a passenger pigeon nesting area in Allamakee County in the 1860s measuring 20 miles long by 2 miles wide, with nests in almost every tree. [8] Habitat loss since the early settlement period has resulted in the elimination of bison, elk, black bear, gray wolf, mountain lion, whooping crane, and passenger pigeon, in addition to the severe reduction of ruffled grouse, American woodcock, river otter, quail, and bobcat. [9]

Today, there is evidence for at least 188 species of birds in Iowa, including Canada geese, bald eagles, turkeys, and turkey vultures. Some species have been successfully introduced or reintroduced, such as the turkey, ring-necked pheasant, and beaver, while other introduced species have fared less well, such as the chukar, Reeves' pheasant, and common quail. The marshes and stream banks provide habitat for beavers, muskrats, turtles, and frogs, while the rivers contain numerous fish and mussel species; however, since their introduction in the early 1990s, zebra mussel infestations have severely affected local mussel populations. [10]

Sugar maple and basswood trees typically are found along the cooler north-facing hillsides, and burr, white, and red oak, shagbark and bitternut hickory, and birch dominate south-facing slopes. Exotic species present within the monument include reed canary grass, buckthorn, and garlic mustard, among others. Herbs and wildflowers, including various ferns, buttercups, anemones, bellwort, wild ginger, mayapple, violets, waterlillies, sunflowers, puccoon, yarrow, and milkweed are common. In the marshes and stream banks are green dragon, sedges, blue flag irises, cardinal flower, sensitive fern, swamp white oak, silver maple, bladder nut, poison ivy, bulrush, and willow. [11]

By providing conditions in which a range of plant and animal communities flourished, the region's varied topography enabled prehistoric societies and cultures to develop and prosper. "Within its perimeters, the stable environment provided protection for the native vegetation and wildlife," stated archeologist R. Clark Mallam in his 1976 dissertation on Iowa's Effigy Mounds, "and offered, through the predictability of its natural resources, shelter and sustenance for hunting and gathering societies." [12] Many of the plant species present within the monument also provided medicinal uses to the inhabitants of the area. [13]

The historical landscape was both a product of natural forces and human endeavor. Prairie fires resulting from both natural and human causes were a common, if not annual, occurrence on the plains, providing rich nutrients to the soil and stimulating the growth of native vegetation. An early description (1871) of prairie fires comes from Charles White's harrowing tale of escape from a tallgrass prairie fire in northwest Iowa. [14] Plains Indians deliberately used prairie fires in their hunting and plant gathering practices to help control the seasonal movement of bison, to promote specific vegetation growth by increasing the "edge effect" and to foster the diversity of habitats. [15]

In much the same way, the extant landscape displays the interconnected influences of cultural and natural components in a continuously evolving relationship. Human societies are linked to the physical environment through the use and adaptation of available natural resources, as environmental constraints help define settlement and subsistence options available to a particular social group. These constraints include proximity to water, climatic patterns, access to lithic resources, and the presence of game and edible plants. Parameters such as these affect site selection for settlements and influence the likelihood of the site's subsequent preservation. Only sites preserved through a combination of environmental and geographic factors remain sufficiently intact to yield information concerning prehistoric peoples. Consequently, the information available about patterns of human occupation in a given area is shaped both by the type of societies that occupied the area and the subsequent and contemporary environmental conditions present at the site.

Aerial view of the Fire Point Mounds. Courtesy of National Park Service