The three counties of Lincoln, Oneida and Vilas are all contained in what geologists refer to as “the central geographical province of the state.” or otherwise, the Northern Highland, which is an upland--part of the Lake Superior Highland, and which at Rhinelander, Oneida County, has an elevation of 1500 feet above sea level, with an annual rainfall of 34 inches. The rock formation, exposed at the surface, is that of the Niagara limestone, a Silurian formation.

The Northern Highland is a peneplain, that is a plain made by the wearing down of ancient mountains, or a region worn down nearly to a plain where formerly there was rougher topography. This peneplain is underlain by pre-Cambrian rocks, including igeous, sedimentary, and metamorphism rocks of Archean and Algonkian age. All the area of the Northern highland was thousands of years ago covered by the continental ice sheet, or glacier. It is thought there were several complete or partial withdrawals of the ice sheet from the Highland, and at the last oscillation, known as the stage of Wisconsin glaciation, a considerable area of the Northern Highland was left un-glaciated, this including a part of Lincoln county. That part of the glacier which covered most of the central northern part of the state, including all of Vilas, all of Oneida and nearly two-thirds of the upper part of Lincoln County, is known as the Chippewa Lobe, while the lower third, south of the irregular line forming the southern boundary of the lobe, belongs to the region of the Older Drift. The out wash deposits cover vast areas in the Northern Highland. The thickness of sand and gravel deposited by streams from the melting ice often exceeds 30 to 40 feet. The stratified gravels form out wash plains of great extent in Vilas and Oneida Counties, in particular near Eagle River.

The Highland Lake District of Northern Wisconsin lies in Vilas, Oneida and adjacent counties, including to some extent the upper part of Lincoln. Are hundreds of lakes in this group. Their total number and closeness of position may be inferred from the fact that, although one of the largest of these bodies of water covers only 6½ square miles, the 346 lakes and ponds of Vilas County occupy 140 square miles, or cover 15 per cent of the area of a county nearly as large as the State of Rhode Island. The northern portion of Oneida County is equally lake-covered. In few parts of the world are there more lakes to the square mile. The lakes as a rule are small, closely spaced, irregular in outline, and are connected by streams which have the most irregular courses. All this is typical of lakes in a glaciated region. These bodies of water are all glacial, but the origins of the lake basins are diverse. Some are shallow depressions in the ground moraine, some are held in by recessional moraines, and some are hollows in the out wash gravel plains. The smaller hollows are kettles formed at the close of the glacial period by the melting of buried ice blocks. Few, if any are in glacially-excavated rock basins, for this part of the state has the rock ledges deeply buried by glacial drift.

Marshes cover about 425 square miles in Vilas, Oneida and adjacent counties, which is about 21 per cent of the area. Open swamps or marshes in northern Wisconsin are often called by the Indian name of muskeg, and of the flat expanses of grassy muskeg, the Flambeau and Manitowish Marshes are among the largest, each covering from 15 to 25 square miles. Their shape in general corresponds more or less to an irregular circle, in which they differ from those to the east in Marinette County, which are long narrow swamps, trending northeast-southwest between the morainic ridges.

The swamps are usually monotonously level. The surfaces are often covered with peat and decayed vegetation. Hardpan underlies the peat, and it is this that causes the marshes, for water easily escapes from sand-floored depressions. There is often sand below the hardpan. The muck in certain swamps is poorly consolidated and some of the muskegs are quaking bogs, especially near the borders of lakes. The presence of this 21 per cent of marsh land in the lake country of northern Wisconsin, together with the sandy soil of the out wash plains and the hilly topography of the terminal moraines that makes a large are in Vilas, Oneida, Iron, Forest and adjacent counties better adapted to being a forest reserve than a region of farms. Half the area is either swampy or has poor soil, and only a little over a sixth of it has good soil. In 1910 only a little over 3 percent of Vilas County was in farms and about 13½ percent of Oneida County. Lincoln County was much farther developed agriculturally.

Samuel Weidman in “The Geology of North Central Wisconsin” (Madison, 1907) says in regard to this region: “In the vicinity of Merrill there is relatively a great abundance of the Third Morainic deposits, as compared with the abundance in other parts of the area of this formation. The knobs and sags are especially numerous in the valley of the Wisconsin River and occur as far southward as the mouth of Pine River. Some of the drift ridges and knobs in the vicinity of Merrill attain a height of 30 to 50 feet above the immediate surroundings.......The northern part of Merrill on the west side of Prairie River is characterized by numerous depressions and bouldery drift.....This locality seems to be an old river bottom, perhaps once occupied by the Wisconsin River whose earlier bed seems likely to have been along the present line of the Chicago, Milwaukee & St. Paul Railway...... Terminal moraine deposits also appear to be unusually abundant in the large valley of the Pine River...... The general result of the Third deposition has been to soften the rugged contours of the earlier land surface..... The course of the terminal moraine in Lincoln County appears to be but a narrow belt two or three miles wide, the highest hill being about 100 feet in elevations.
(Jones, George O., Norman S. McVean, and others, comp. History of Lincoln, Oneida and Vilas Counties Wisconsin (15pt) Minneapolis, MN: H. C. Cooper, Jr. & Co., 1924. Transcribed and edited by Jack L. Winegar.