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<br />Environmental Setting
<br />The landscape of the project region is dominated by features associated with the advance of the Superior ice lobe
<br />and the later Des Moines lobe during the Late Wisconsinian glaciation (ca. 35,000 to 10,000 years ago). As a result
<br />of the area's glacial history, lithic raw materials suitable for the manufacture of stone tools would be available
<br />locally from sources within the glacial till, or nearby glacial outwash sediments. The southernmost extent of the
<br />Superior lobe, which originated in the Lake Superior basin, is marked by the eastern St. Croix moraine complex.
<br />The complex, including the project area, is a broad band of hilly topography stretching northeastward from St. Paul
<br />into Wisconsin (Wright 1972). The glacier's legacy in the project vicinity is a reddish, gravely till that when
<br />reworked forms coarse, droughty and relatively unfertile soils (Wovcha et al. 1995:6). The reddish till in vicinity of
<br />the project is mantled by a thick deposit of newer till material, left by the most recent glacial episode.
<br />The last major glacial episode to affect the region was the advance of the Des Moines lobe from the region of
<br />Manitoba. An extension of this coverage known as the Grantsburg lobe spread out along the interior margin of the
<br />St. Croix moraine, covering the project area and leaving a deposit of light olive -brown loamy till commonly known
<br />as "gray till" (Chamberlain 1977:87; Wright 1972b: 534). Soil developed from the grey till tend to be loamy and in
<br />contrast to the red till left by the earlier Superior advance, retain moisture very well (Wovcha et al. 1995:7). The
<br />Grantsburg sublobe retreated ca. 16,000 to 13,000 years ago-providing the sandy outwash material from which the
<br />Anoka Sand Plain is formed. The Centerville chain of lakes in southeastern Anoka County, in which the project
<br />area is located, demarcate drainageways left by the Superior lobe. These lakes form the approximate boundary
<br />between the eastern St. Croix moraine and the Anoka Sand Plain. As noted above, the topography of the St. Croix
<br />moraine is hilly with differences in relief most marked toward the northeastern limit of the complex in Wisconsin.
<br />Scattered within the rugged morainic topography are numerous wetlands and lakes formed by ice blocks that broke
<br />off from the retreating glacial ice and were subsequently covered by till.
<br />Dramatic changes in the regional environment have occurred during the course of its postglacial history. A
<br />periglacial parkland of spruce and larch closely followed the retreat of the Wisconsinian ice sheets and their
<br />periphery of tundra vegetation. By 11,500 years ago, rapid climatic change had caused the spruce forest to
<br />disappear from the state. It was succeeded by pine forest by 10,000 years ago and then by a deciduous forest
<br />comprised primarily of oak and elm. The warming and drying trend of the early to middle Holocene peaked at
<br />7,000 to 6,000 years ago, at which time the prairie and its border strip of deciduous woodland had expanded to 75
<br />miles north and east of their historic limits. Linked with these climatic and vegetational trends were an increase in
<br />the frequency of prairie fires and a dramatic decline of the water table, causing many small lakes to dry up
<br />completely. A return of more moist and cool environmental conditions approximately 5,500 years ago resulted in
<br />the establishment of the prairie- forest border near its present limits (Anfinson and Wright 1990; Grimm 1981;
<br />Wright 1974).
<br />Environmental data are available for the larger vicinity of the project area from the Middle Holocene to the present,
<br />through pollen analyses at Wolsfield Lake and Wosfield Marsh in Hennepin County (Grimm 1981, 1983). Those
<br />investigations suggest that woodland existed throughout the Holocene in the northeastern Big Woods (including the
<br />project area). It is perhaps best accounted for through the local infrequency of fire due to the rolling topography
<br />and numerous deep lakes which would have retained water even in the dry middle Holocene. Local vegetation
<br />consisted of woodland and prairie in approximately equal parts from 6,330 to 3,810 years ago, and was succeeded
<br />by oak - dominated woodland from 3,810 to 280 years go. The onset of cooler and wetter climatic conditions aided
<br />the development of the true Big Woods forest dominated by elm, maple, and basswood, from 280 to 95 years ago.
<br />The effects of Euro - American clearance and settlement are then seen, extending to present day (Grimm 1981,
<br />1983).
<br />Oak woodland- brushland dominated the vegetation of the St. Croix moraine at the time of Euro - American
<br />settlement in the mid - nineteenth century. Species represented included northern pin oak, bur oak, white oak, and
<br />aspen trees, with an understory of young oak and aspen, hazelnut, and prickly ash (Wovcha et. al 1995:26). More
<br />detailed information from the General Land Office survey records indicate a pattern of larger trees and less fire -
<br />resistant Big Woods species (e.g., ash, elm, maple) north and east of lakes in this region, while smaller and more fire
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