Riverside Park

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Devonian Dolomite — 390 million years old — Devonian Period. The youngest bedrock in Wisconsin. This limestone, great for building, was once quarried near what is now the UWM parking lot on Capitol Drive.

Silurian Dolomite — 420 million years old — Silurian Period. Formed from coral reefs and shells of sea animals this rock runs along the eastern edge of Wisconsin then dips below Lake Michigan to rise all the way over in Niagara Falls!

Cambrian Sandstone — 510-520 million years old — Cambrian Period. Wisconsin once lay near the equator, covered by shallow tropical seas. Rock from this period is in the gorges and cliffs of Wisconsin Dells.

Basalt — 1.1 billion years ago — Middle Proterozoic Eon. When the earth’s crust in northwestern Wisconsin began to tear apart it threatened to tear North America in half and basaltic lavas erupted. Basalt is used for building railway lines and road bases or, when cut and polished, for floor tiles.

Red Sandstone — 1.1 billion years old — Middle Proterozoic Eon. Pre-dating any evidence of fossils, it’s tinted by iron oxide from the first rising of oxygen in ancient seas. It’s known as the Keweenaw Sandstone and was quarried during the 1800’s “brownstone” era of architecture.

Baraboo Quartzite — 1.7 billion years old — Lower Proterozoic Eon. This started as pure quartz sand and after hardening into sandstones, it then was changed by pressure and heat to pink, maroon and purple by iron particles. Smoothed, rounded monadnocks of quartzite as much as 4000 feet thick are in Rib Mountain.

Red Granite — 1.8 billion years ago — Lower Proterozoic Eon. Granite gneisses formed the beginning of North America. When Wisconsin was covered by a sea and a chain of volcanic islands, the islands collided with the old continent, causing Penokee Range of north-central Wisconsin. Red granite is the Wisconsin state rock.

Banded Iron Formation — 1.9 billion years ago — Lower Proterozoic. Formed in lagoons or shallow coastal waters where dissolved iron in sea water interacts with free oxygen and magnetite (iron oxide) mixes with chert (silica) to settle to the sea floor in layers of hard sedimentary rock. You can see this formation along Lake Superior.

Nephrite Jade — Precambrian Eon. Jade is Precambrian as is the banded iron on this cairn. This is from the oldest era of Wisconsin, perhaps as old as 3 billion years!