The sand and gravel deposits in Boone and McHenry counties are also attributed to the glaciers. These are some of the most valuable and productive in the state, supplying tons of construction aggregates to the Chicago area. As the meltwater from the glaciers gushed off the top, front, and from beneath the ice sheet, sand and gravel were flushed out or carried beyond the glacier by the meltwater torrents. The material is called outwash.
The geology of the area, however, is not confined to what is visible to the naked eye. One hundred feet below the surface lies another landscape, complete with rolling hills, flat plains, and valleys. The Troy Valley and its tributaries traverse most of the assessment area. A major valley that drained parts of southern Wis­consin and northern Illinois during the Pleistocene, most of it is entrenched in bedrock and is covered with till. It is impossible to tell from the surface topography that a deeply incised bedrock valley lies below. The Troy Bedrock Valley can still be seen in southwestern Boone County, where it merges with the Kishwaukee Valley. As the Troy became blocked by glacial ice, meltwater was diverted to the west across a dolomite ridge. The major concentration of flow cut the narrow 150-feet deep gorge through which the present Kishwaukee River flows.

Several Natural Areas and a quarry highlight the geology of the Kishwau­kee area. Flora Prairie in Boone County has dolomite outcrops. Har­vard West Geological Area in McHenry County has an example of pitted outwash plain while Harvard East Geological Area is an example of a moraine protruding down a valley. On Illinois Route 20, near the Boone/ McHenry County line, is an aban­doned quarry. This area has the distinction of having the only bedrock exposures in McHenry County and is a 'bedrock high' along the margin of the Kishwaukee River; it stands about 25 feet above the general valley level. When the first geological surveys of the county were conducted during the 1860s, stone was already being quarried there.

Early Inhabitants
'The mound builders whoever they were, once swarmed in the valleys and woodlands, sat down upon every picturesque spot along the streams, and left their mound-builded structures as memorial monuments of their busy lives. ... But the locality where they are met with in the greatest numbers is on the banks of the Kishwaukee, in the southeastern part of the county near the confluence of the two streams of that name.

James Shaw, 1873
Geology of Winnebago County in the Geological Survey of Illinois, Volume 5

During the waning stages of the Ice Age, the first Native Americans began to arrive in Illinois. Settlement first occurred along many of the state's rivers and streams, and the Kishwaukee was no exception. The archaeological data base for the Kishwaukee River basin indicates that the region was continuously occupied for the last 12,000 years, in spite of major changes in both social and physical environments. A total of 560 archaeological sites have been recorded for the Kishwaukee area and range in age from Paleo-Indian (10,000 B.C.) through the Postwar Industrial period (1946 A.D.).

The first investigations of the region were of the mound sites. The westernmost end of the drainage near the Rock River valley includes several mound sites of Mississippian (900 A.D.) or Upper Mississippian (1400 A.D.) cultural affiliation. James Shaw wrote, "Scores of them are scattered about here, and scores more have been nearly obliterated by the sacrilegious ploughshare of the white man. The oldest inhabitants recall many oc­casions where bands of Indians, pilgrim-like, returned to these silent mounds, and held over them for days their mystic pow-wow."

No sites with historic Native American (1650 A.D.) components have been identified, although the area was occupied by these native peoples. The Mascouten occupied the area at the time of earliest contact with EuroAmericans at about 1655. Over the next 150 years the area was claimed as territory by various Miami-speaking groups and the Potawatomi. By 1840 all the Native American groups had been removed to more westerly reservations.

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