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

Several outcrops of a variety of Precambrian rocks occur in Waupaca. They include:

  1. Fine-grained pink granite on Granite Street
  2. Dark, fine-grained intrusive rocks at Rasmussen Park
  3. Metamorphic rocks along the Waupaca river
  4. Fine-grained probable metavolcanic rocks at a flooded quarry (now a park).

Granite Street

Fine-grained pink granite outcrops along Granite Street. If the name "Granite Street" seems a bit obvious, bear in mind that a lot of people in Wisconsin refer to Baraboo Quartzite as "granite."

Rasmussen Park

The panorama below shows the park. Both fine-grained dark intrusive rocks and pink granite occur. A large erratic of Waupaca rapakivi adamellite is visible at the left top of the hill. There are undisputed granitic rocks a few hundred meters to the west on Granite Street, metamorphic rocks a couple of hundred meters to the east along the river, and this appears to be a contaminated border facies. It is very similar to the petrology along the northern margin of the Wolf River Batholith at High Falls Dam

A pinkish, granitic phase
Dark, fine-grained rock cut by a small granitic dike
A somewhat coarser, dark intrusive phase, very similar to the dark border rocks at High Falls Dam.
Above and at left are three general views of the outcrops

Waupaca Adamellite

This rock type, a perfect example of a rapakivi granite, is not exposed here (although it is at a small quarry north of town). At left is the erratic, below are close-ups of the coarse (2-3 cm) feldspars, often rounded by abrasion during magmatic flow. Rapakivi granites, named for a locality in Finland, have plagioclase cores rimmed with potassium feldspar, and many of these feldspar crystals show that texture.

At right below, note the differential weathering. It is frustratingly hard to get good samples of this rock. Convenient samples are crumbly, solid samples are too big to move.

Waupaca River

The outcrops are located in the river and woods northeast of the municipal garage on Water Street. 
There is a small park on the river bank. The outcrops begin just north of the parking lot. Views of the outcrops are below.
This is a view looking north from the bridge. The outcrops begin about at the distance of the truck.

Outcrops on the River

The outcrops in the river and on the riverbank are pinkish on weathered surfaces. They generally show a weak subvertical N-S foliation 

Outcrops in the Woods

Above and left: general appearance of the outcrops in the woods. They are best seen when the leaves are gone and even then, getting at them involves clawing through brambles.

Intrusive Rocks

  Outcrops in the woods away from the river show generally uniform texture with numerous small dikes and veins and are probably intrusive. The contact probably runs roughly parallel to the river and just west of it.
This outcrop shows a contact and a very obvious xenolith.
Uniform fine-grained rocks with dikes
Uniform fine-grained rocks with dikes

Foliated Rocks

Outcrops in the woods closest to the river have a crudely gneissic appearance.

Quarry Park

A view of the park. It's reached most easily by walking along the railroad tracks.
A trail leads around the quarry.
Much of the rock here is pinkish, fine-grained, and uniform.
On weathered surfaces the rock sometimes has a banded or foliated appearance. Thus, it is not intrusive, but more likely metavolcanic. These rocks are similar to the outcrops in the Waupaca River.

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Created 3 May 2002, Last Update 11 Jan 2020