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The Central Plain of Wisconsin
The Central PlainIf a traveler, on his way from eastern United States to the Pacific coast, be fortunate enough to cross central Wisconsin by daylight, he will pass through the village of Camp Douglas [western Juneau County] or the village of Merrillan [northern Jackson County]. For many miles nearby, he may see landscape features totally unlike those anywhere else in the United States east of the Mississippi River. The hills of the region near Camp Douglas are buttes and mesas. They have the straight lines, steep cliffs and sharp angles of an arid country rather than the soft curves of a humid region.
The features to be seen are (a) isolated, rocky hills which resemble ruined castles, (b) grotesque towers and crags of sandstone along a line of bold, irregular bluffs, and (c) an unusually flat plain which stretches away beyond the northern and eastern horizons. The bluffs and steep slopes on the west and south form the escarpment at the border of the Western Upland. The level country is the Central Plain of Wisconsin.
The irregular bluffs are part of an escarpment capped by resistant rock. The isolated castles and crags are outliers of the escarpment, left behind in its recession to the south and west under the attack of weather, wind and streams. The flat plain has been made by the wearing down of weak and nearly- horizontal sedimentary rocks, and by deposition of unconsolidated materials upon the surface.
Absence of glacial erosion and of direct glacial deposition make it possible for the rather fragile rock forms produced by weathering and wind work to persist and to dominate the landscape. These forms near Camp Douglas and Merrillan are not repeated westward until the Great Plains in the Dakotas and Montana, and even these are partly in glaciated territory.
The evergreen trees, clinging in precarious positions on the rocky buttes and mesas of the Camp Douglas Country, and the tamaracks on the swampy, level plain, are among the first forerunners of the northern forest. They furnish a notable contrast to the open prairies near the Great Lakes and to the deciduous trees of the East and South. The evergreen trees show definitely, however, that the region near Camp Douglas is not arid. The sandy soil makes the precipitation less effective because much of the rainfall sinks into the ground at once. Wind work is dominant, not because we are in arid lands but because we are in a sandy part of the Driftless Area. The smaller plants on the hills at Camp Douglas, and at other places in the Driftless Area, includes several types of dwarf cacti such as the prickly pear. The evergreens, suggesting the North, and the spiny plants, suggesting the West, mark this as a frontier region for the traveler.
Large parts of the Central Plain are decidedly unlike the Camp Douglas Country. Where there is less alluvial filling, the Central Plain is more hilly. Where there has been glaciation, the buttes and mesas are few or wanting. The swamp which stretches northeastward from Camp Douglas is two- fifths as large as the state of Rhode Island, but only a small proportion of the Central Plain is swampy. The soil near Camp Douglas and Merrillan is sandy so that farms are poor and settlement therefore sparse, but parts of the Central Plain are densely populated. Instead of corn or wheat, the crops are apt to be potatoes, buckwheat, oats, rye, barley and cranberries.
In the eastern part of the Central Plain the Indians lived long before white men came to Wisconsin. In the late 1600s Father Marquette wrote of an Indian village in this area:
"I took pleasure in observing the situation of this village. It is beautiful and very pleasing; for, from an eminence upon which it is placed, one beholds on every side prairies, extending farther than the eye can see, interspersed with groves or with lofty trees. The soil is very fertile and yields much Indian corn."
General Description of the Central Plain
The Central Plain of Wisconsin is a crescent- shaped belt covering about 13,000 square miles. All of it is floored by the weak Cambrian sandstone, except in the northwest where the removal of the sandstone has exposed the underlying Keweenawan lavas for a small area. The surface elevation ranges from 1242 feet at Cumberland, Barron County, in the western part of the crescent, to 785 feet at Portage, Columbia County, in the central part of the plain, and 685 feet at Ellis Junction, Marinette County, near the eastern end of the lowland. the general slope from place to place is very gradual indeed. For example, in the 65 miles from the northern to the southern edge of the plain, the grade is only 4-1/3 feet to the mile.
The local relief varies considerably, but except for a few isolated hills it is nowhere great. The Central Plain is not all a continuous plain, but in many places is a region of low hills, as northwest of Wisconsin Dells, north of Tomah, south of Pray and southeast of Black River Falls. Parts of the plain are due to (a) smooth river deposits, (b) lake- bottom accumulations, (c) vegetation in swamps, or (d) glacial drift.
An excellent place to see the variety of features of the Central Plain is from Saddle Mound south of Pray Tremont in Jackson County. This hill rises more than 400 feet above the surrounding lowland, its crest being more than 1400 feet above sea level. To the southeast lies a vast, monotonously even plain of lake deposits. To the southwest is an equally level plain of non- glacial alluvium, stretching away till it terminates at the blue wall of the Western Upland. In the immediate foreground are low, rounded hills of sandstone. Such resistant layers as cap Saddle Mound have been removed from the adjacent hills by weathering and erosion, so that they have been reduced to old age in their erosion cycle. Scrub timber grows in bunchy groups. There is no grass, and the white sand appears between the shrubs. The hill slopes disclose vertical cliffs, angular profiles, flat- topped ridges, teepee buttes, much as on parts of the Great Plains. Side by side are vast, swampy plains which need ditches to drain away the water, and sandy plains and low slopes which need water.
The group of hills east of Millston, Jackson County, preserves a large sample of the topography that characterized the Central Plain before the Glacial Period. They are high enough to rise above the alluvial and lacustrine plain. they have moderate slopes, occasionally with steep cliffs. At one point six miles east of Millston there is an extensive deposit of rounded, preglacial gravels. Little, if any, of the Central Plain had level topography before it was smothered in the glacial outwash, lake clay and alluvium. It was everywhere a region of slight relief, however.
Topography and Origin of the Central Plain
All the characteristics of the sandstone plain are normal to an inner lowland of a belted plain. The name inner lowland is used in connection with slightly- dissected coastal plains. Where uplift takes place in a coastal plain, made up of alternate layers of weak and resistant rock which dip gently toward the ocean, it will be carved by streams and the weather as follows: An asymmetrical ridge underlain by resistant rock, if of small dimensions and steep dip, is referred to as a monoclinal ridge. Large monoclinal ridges are called cuestas (see above). The belt of weak rock between the inner cuesta and the partly exhumed oldland or backland is the inner lowland.
In eastern Wisconsin the Cambrian sandstone dips rather steeply and is thinner than in the central part of the state. Accordingly the inner lowland is narrow. Its width in Marinette County is only a little more than five miles, but in Clark, Jackson and Monroe counties, where the sandstone dips less steeply and is thicker, the width of the inner lowland is 50 miles. The width of the lowland seems to be chiefly determined by the erosion surface as related to the dip of the sandstone.
The elevation of the Central Plain varies considerably. In Marinette and Oconto counties heights of 801 feet above sea level at Gillett and 685 feet at Ellis Junction constitute the lowest part of the sandstone plain. On divides near the edge of the pre- Cambrian peneplain the Central Plain is high, while in river valleys near the edge of the limestone upland on the other side it is low.
Rising above the sandstone plain in places are numerous, usually flat- topped ridges and hills, often bearing the name "mound." They are very abundant in the region north and west of Wisconsin Dells, in the vicinity of Camp Douglas, and in many other portions of the Central Plain. Most of them lie within the Driftless Area. These so- called mounds have simple rock structures, flat tops and cliffed sides. The craggy side of the mounds often look, from a distance, like ruined castles and towers, as at Roche a Cri in Adams County north of Friendship. Roche a Cri stands about 300 feet above the adjacent plain, its crest being about 1185 feet above sea level. It is a long, narrow, flat- topped ridge bordered by sheer precipices. It is probably the steepest hill in Wisconsin. It is also one of the most conspicuous and beautiful.
Friendship Mound, southern neighbor of Roche a Cri, rises 85 feet higher, but is a much less striking topographic feature. From Roche a Cri one sees scores of sandstone crags and towers, such as Pilot Knob, Mosquito Mound, Bald Bluff, Long Mound, Bear Bluff, Rattlesnake Mound and Dorro Couche.
A dozen miles to the west are Petenwell Peak and Necedah Mound. The former is a cragy ridge of sandstone, its summit well- nigh inaccessible. The latter is a rounded knob of quartzite, easily ascended. Necedah Mound is a partly- exhumed monadnock of the pre- Cambrian peneplain.
Three stages in the erosion cycle are well represented by Friendship Mound, Roche a Cri and Petenwell Peak. The first will eventually be reduced to the stages represented by the other two, but not until Petenwell Peak has been completely destroyed by weathering and erosion.
The capping material which forms the flat tops of these buttes and mesas is one of several resistant sandstone layers, which is better cemented than the average. That certain layers in such a soft and relatively weak rock as the Cambrian sandstone should stand up in places in precipitous cliffs, irregular crags and towers, is due partly to the porosity of the rock, partly to its lack of limy and shaly beds, and its thick- bedded character. Weathering and wind work are going on rapidly around the borders of these tabular hills. The sandstone breaks down along vertical joints, the rock falls to pieces, and is blown and washed away.
When the resistant cap is removed by weathering and the prevalent wind work, the buttes soon wear down to conical hills. These are well seen in the hills south of Pray as well as in Monroe county east of Sparta, in a valley of the Western Upland, where there are many teepee- buttes, rising 100 to 150 feet above the adjacent plain.
Changes Due to Glaciation
The ice of the continental glacier advanced over the Central Plain of Wisconsin from both the northeast and the northwest, but an intermediate portion of the inner lowland in Wood, Portage, Adams, Juneau, Monroe and Jackson counties was not overridden by the glacier. In this portion of the Driftless Area, except for the low areas mantled by stream and lake deposits, are found the topographic forms which must have characterized the whole geographical province before the Glacial Period.
Except in the sandstone counties west of Green Bay, the depth to which the continental glacier eroded the surface of the Central Plain was relatively less than in many other parts of Wisconsin, though it was by no means negligible. The glacier must have removed hundreds of outlying mesas and buttes, and thousands of smaller pinnacles similar to Stand Rock, for these forms are now virtually limited to the Driftless Area. Before the Glacial Period they must have existed in vast numbers throughout the whole Central Plain.
Where the weak sandstone lay in the direct path of a rapid current of the glacier, the ice eroded deeply and scoured out lake basins. Green Lake, for example, is partly in the sandstone plain and partly in the limestone cuesta. Its valley was eroded to a depth of 300 to 450 feet by glacial erosion. The lake is 237 feet in depth, being the deepest inland lake in Wisconsin.
[At the eastern edge of the Central Plain], a view from the summit of Mt Morris, Waushara County, furnishes a striking contrast to the prospect from Roche a Cri. Roche a Cri is in the Driftless Area, but Mt Morris is in the midst of glaciated territory. Its flat top is bestrewn with granite boulders, carried there by the ice. Its moderately sloping sides reveal ledges of sandstone, but there are none of the crags and pinnacles that must have characterized the hill before the Glacial Period. The plain is not smooth, but slightly irregular, with gently- undulating ground moraine, rougher terminal moraines and outwash plains containing deep kettles and many valleys eroded since the outwash was deposited. The most striking contrast with the view from Roche a Cri is that almost no rock hills are to be seen from Mt Morris.
Bald Bluff and the adjacent hills repeat the same story. they overlook a vast expanse of country devoid of rock hills. The rare exceptions, like Bald Bluff, were left because they lay near the thin, weak edge of the ice.
The drift deposits of the Central Plain are similar to those in the Western Upland and the Eastern Ridges and Lowlands except they are decidedly more sandy.
In contrast with the numerous glacial lakes in eastern Wisconsin, there are relatively few lakes in the Central Plain. This is chiefly because the depressions produced by glacial erosion and by irregularities in the drift are sandy- bottomed and, therefore, do not generally hold water. Where moraines are more abundant, lakes do occur, as in Burnett, Polk, Barron and adjacent counties in the northwestern part of the Central Plain, and parts of Waushara County in the east.
The till sheet of the Wisconsin stage of glaciation in the eastern portion of the Central Plain is thick, concealing nearly all the rock ledges. Parts of Outagamie, Waupaca, Waushara and Winnebago counties contain deposits of red clay. These are similar to those laid down in a glacial lake and subsequently ridged up into ground moraine or terminal moraine by the readvance of the Green Bay love.
A few castellated hills rise through the morainic deposits as nunataks. These are hills where were once completely surrounded by the ice, though never overridden. They are limited to the border of the glaciated region where the ice was thin. The castellated bluff or mesa or iron- stained sandstone at Humbird, Jackson County, is one of the most accessible of these nunataks. The ice of the continental glacier wrapped completely around the foot of this nunatak, then terminated less than a mile to the southwest. The Neillsville nunatak in Clark County is of the same character as the one at Humbird. Both are surrounded by glacial debris.
The kettle moraine at the eastern border of the Driftless Area is an exceptionally broad, irregular accumulation, well seen (a) north of Baraboo and Wisconsin Dells, (b) east of Hancock, and (c) near Amherst Junction east of Stevens Point. South of Waupaca the recessional moraines of the Green Bay lobe form conspicuous ridges.
Near the St Croix Dalles, Polk County, there are two sets of terminal moraines. Remarkable as it may seem, the glacier was moving toward the northeast at this point.
The deposits made by steams from the melting ice sheet cover large areas in the Central Plain. The streams laid down sand, clay and gravel, not only in the actually glaciated region, but in the otherwise Driftless Area as well. These deposits attain thicknesses of 100 to 200 feet or more, as at Necedah. Many of them have smooth, gently- sloping surfaces, as in the region between Wisconsin Rapids and Wisconsin Dells and to the northwest of Baraboo. Opposite certain gaps in the terminal moraines are broad alluvial fans of outwash gravels. These indicate some of the later stream channels occupied by the glacial rivers which deposited the outwash.
The deposits of former glacial lakes cover parts of the Central Plain, in the driftless as well as the glaciated area. These lakes were apparently short- lived, for they produced few well- defined shorelines. The existence of these bodies of water is proved by the finding of lake- bottom sediments, as near Grantsburg in Burnett County, and Menomonie in Dunn County, where the clays are used in making brick.
The largest area of lake deposits is on the bed of Glacial Lake Wisconsin. This former body of water left lake deposits over an area of more than 1,825 square miles. The lake deposits are covered in many places by glacial outwash, by dune sand, by peat and muck, or by alluvium. In the northern and northwestern part of the basin, the lake deposit is white quartz sand. The glacial streams flowing into Glacial Lake Wisconsin from the north deposited their coarsest detritus near shore. The sand was carried offshore in suspension and deposited evenly over the bottom of the glacial lake. The clay was deposited still farther to the south.
Similarly, the glacial torrents flowing into this lake from the east deposited their coarse materials in the outwash plains east of the lake, as in the great gravel pit southeast of the village of Grand Marsh, Adams County. The finer detritus was carried offshore and spread over the lake bottom as a mantle of limy clay.
The deposits of Glacial Lake Wisconsin include isolated, erratic boulders of granite, greenstone and other crystalline rocks, for example in Juneau County west of Wisconsin Dells, and in Sauk County west of Baraboo. Our best evidence of the height of the lake surface comes from these ice- rafted erratics. Near Baraboo and Wisconsin Dells they do not occur above a level of about 960 feet.
To the northwest, rounded sandstone and chert boulders are found in a beach deposit on Mile Bluff south of Mauston. The deposit is less than 980 feet above sea level. Erratics have been found to the southwest near Reedsburg, where there was a bay of the glacial lake.
Some of the best beach deposits of Glacial Lake Wisconsin are on islands, including numerous erratics on the quartzite mound four miles northwest of Babcock in Wood County.
The levels at which erratics and beach gravels are found, show that the shorelines of Glacial Lake Wisconsin may not be horizontal at present, but rise toward the north. They appear to increase in altitude from 960 feet near Baraboo and Wisconsin Dells to almost 1000 feet 55 miles to the north near Babcock and City Point.
The swamps of central Wisconsin were formed as a result of the accumulation of the more impervious deposits of Glacial Lake Wisconsin. Although the marshes, bogs and other swamps of Wisconsin are chiefly in the area of latest glaciation, the largest swamp in the state happens to be in the Driftless Area. It lies in the area between Wisconsin Rapids, Camp Douglas and Black River Falls, covering about 30,000 acres. It is more than twice as large as Milwaukee county.
On the whole, the soil of the glaciated portion of the Central Plain was improved by the importation of the drift with limy rock flour, limestone boulders and various crystalline rocks from the region outside. The sandy soil of the driftless portion of the plain and the areas covered with outwash or dune sand are far less productive than the part of the plain covered with limy, sandy and stony glacial till, or with loess and lake clay.
[The Dells of the Wisconsin, the Lemonweir and Yellow Rivers, the Fox River system (including the Wolf river), the Black, Chippewa and St Croix rivers, and the Fall Line Cities of the Central Plain are discussed in detail beginning on page 345 of the book.]
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