Mosquito Hill

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

Location: 3 km E of New London, 0.5 km S of County S, NE 1/4, SE 1/4 section 33, T22N, R15E, New London 7.5' Quadrangle.

Mosquito Hill is one of several steep hills in the New London area that consist of Cambrian Jordan sandstone protected by a cap of Oneonta (Prairie du Chien) dolomite.

Turn south at the sign for the Mosquito Hill Nature Center. Proceed to the end and park. The Nature Center is delightful and well worth a visit. In addition to trails on Mosquito Hill there are also numerous trails to the Wolf River. 

From the parking lot, follow the trail northeast to the base of the hill. Follow the left branch of the trail. It curves around the northern side of the hill, then switches back to the main outcrops on the western end of the hill. Numerous plutonic rock erratics are visible along the trail as well as outcrops of Cambrian sandstone along the upper switchback. A small bench in the western end of the hill, probably once a small quarry, offers a good view of the outcrops plus an overlook of the surrounding area. 

The base of the hill is made up of Cambrian sandstone, which is poorly exposed. The top is Ordovician Prairie du Chien dolomite. This resistant cap protects the soft rock below from erosion. If we were out West we would call this hill a mesa. Outcrops of Cambrian sandstone can be seen in places along the trail up the north side of the hill.

A view from the top of Mosquito Hill looking west over the city of New London
A view from the top of Mosquito Hill looking northwest. The low hills in the foreground are glacial deposits.

At this locality the contact is somewhat gradational over several meters, representing a transgressional sequence of sandstone giving way to sandy dolomite, then massive dolomite (Smith et al.,1993). The sandstone is probably the Van Oser Member of the Jordan Formation, a moderately well sorted, fine- to medium- grained, brown to tan quartz arenite with pink, somewhat degraded feldspar grains. The sands are usually fairly well cemented and often display trough cross-bedding.

The sandstone is overlain by sandy dolomite, probably the Stockton Hill Member of the Oneota Formation. Above the sandy dolomite is light gray to buff thin-bedded, crystalline dolomite with occasional vugs containing crystals of dolomite. Fossils are scarce at this location. These beds may, all or in part, belong to the Hager City Member. That unit is relatively clean dolomite with less sand and silt than the Stockton Hill, although a detailed study has not been carried out.

At the west end of Mosquito hill is a prominent bench, the remains of an old quarry. The quarry extracted the dolomite for aggregate and road fill. At the base of the bench is rather massive sandy rock, grading upward into less sandy and more thinly-bedded dolomite.

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Created 1 July 1999, Last Update 24 February 2001