The formation of the Great Lakes is the result of numerous geological events, the most recent of which involved massive Ice Age glaciers. Many people assume that when the last glacial ice melted—roughly 10,000 to 12,000 years ago—the modern landscapes of Lake Michigan, the Niagara Escarpment, and the Door Peninsula were revealed. In reality, the retreat of the glaciers triggered a complex series of changes. Post-glacial lakes formed and disappeared over thousands of years, gradually shaping the landforms we see today.
At our Ida Bay Preserve, visitors can observe evidence of four distinct post-glacial lakes. Until about 3,000 years ago—give or take a few centuries—much of what is now Crossroads at Big Creek lay beneath water. We speculate that the land at our Cove Estuary Preserve has likely been above water for less than 2,000 years.
Our geological history connects directly to many of the activities we will offer this week. Whether you're joining the Four Bridges Hike, taking part in an Environmental Exploration program, attending a Current (Environmental) Events discussion, or simply observing migrating birds, the legacy of glaciers continues to inform our understanding of the natural world. Even decisions about which native trees to plant as a part of our restoration efforts are influenced by this ancient glacial past.
At a recent Science Saturday program, a young participant asked, “What would Door County be like if there had never been glaciers?”. While geology always involves a degree of speculation, we can glimpse an answer by looking to southwestern Wisconsin—a region known as the Driftless Area.
In the preface to her book Shelter and Storm: A Home in the Driftless, Tamara Dean describes this glacially untouched land:
“A few miles west of Madison begins a landscape like no other on the planet. The Driftless Area is so improbable that from the earliest surveys in the 1800s and as late as the 1980s, some geologists refused to accept its existence. How could all of North America’s glaciers—probably dozens—have bypassed this 8,500-square-mile tract that was neither higher in elevation nor more porous than surrounding areas? Scientists puzzled over the clues for more than 150 years.
“Their conclusion points to a series of extraordinary coincidences. The ice sheets encountered warmer temperatures and melted before reaching the region, or they lost momentum or found easier paths….. During the Wisconsin Glaciation (which lasted from roughly 60,000 to 10,000 years ago), some glacial lobes followed the basin now occupied by Lake Michigan. Encountering less resistance moving southward, they didn’t spread very far west. Other lobes followed the deep trough of what is now Lake Superior, which prevented them from gaining the momentum to move further south.
“An absence of drift—glacial deposits like pebbles and silt—gave the region its name. Evading the glaciers also preserved its remarkable natural beauty.”
We are pleased to host Tamara Dean at Crossroads at 7:00 on Thursday, May 8, for an Author Talk and Book Signing. Her newly released book invites readers to reflect on how we care for the land, our responsibilities to one another, and how we thrive together in uncertain times. Following the presentation, copies will be available for purchase from Novel Bay Booksellers.
Like the Driftless Area, the Door Peninsula boasts remarkable geological features, and spring is a perfect time to explore them. We look forward to welcoming you to our preserves this spring as we continue to explore, learn, connect with, and restore the land shaped by glaciers, time, and community.
Saturday, May 3
2:00 pm Science Saturday: Four Bridges Expedition
This family-friendly hike explores four bridges and areas of the preserve that were once submerged under post-glacial lakes. It is designed for students, but curious learners of all ages are welcome. Meet at the Collins Learning Center, Crossroads at Big Creek, 2041 Michigan Street, Sturgeon Bay.
Monday, May 5
1:30 pm Current (Ecological) Events Group
At the final session this spring, participants will read and discuss articles related to biodiversity, geology, and climate change. You can pick up free copies of the articles at the Collins Learning Center, but you need not read them to attend, nor are you required to read them before the discussion. Meet at the Collins Learning Center, Crossroads, 2041 Michigan Street, Sturgeon Bay.
Tuesday, May 6
3:30 pm Environmental Exploration: Macroinvertebrates
This after-school program introduces elementary students (and learners of all ages) to the fascinating world of pond-dwelling macroinvertebrates. Meet at the Collins Learning Center, Crossroads, 2041 Michigan, Sturgeon Bay
Wednesday, May 7
1:30 pm Wandering Wednesday
Join a free, naturalist-led walk through the Crossroads Big Creek Preserve. The pace is easy and welcoming to all. Meet at the Collins Learning Center, Crossroads, 2041 Michigan Street, Sturgeon Bay.
Thursday, May 8
7:00 pm Author Talk and Book Signing with Tamara Dean
Join us for a presentation by the author of Shelter and Storm, a Home in the Driftless, an inspiring book of essays describing how we care for the land, our responsibilities to one another, and how we thrive together in uncertain times. Copies will be available for purchase from Novel Bay Booksellers after the program. Meet at the Collins Learning Center, 2041 Michigan, Street Sturgeon Bay.
