Dells Of The Eau Claire River State Natural Area

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The Dells of the Eau Claire River protects a scenic, narrow rocky gorge and waterfalls where geologic processes have resulted in an unusual tilting of bedrock. On this picturesque stretch of the Eau Claire River, the river cascades over outcrops of Precambrian-age rhyolite schist. The rhyolite schist, a very hard rock, was formed through metamorphosis and later tilted here to a nearly vertical position allowing the rock to split readily along the cleavage planes. In the dells, the river tumbles and spills across the rock's cleavage planes while it runs smoothly in other areas where the river flows parallel to the planes. The water current through the dells has been strong enough to produce a series of potholes, formed by the grinding action of swirling sand and gravel. Downstream the flow is quite tranquil. This is an excellent area to observe fracture controlled stream flow and the development of multiple stream terraces. The rocky gorge and forested areas are wooded with a northern mesic forest of hemlock, sugar maple, yellow birch, and mountain maple. Canada yew is abundant in dense patches and the spring flora is rich. The Dells of the Eau Claire is owned by Marathon County and was designated a State Natural Area in 1973.