This geological site is easy to overlook. It’s simply a small rise of exposed rock along a back road in northern Wisconsin, near a town known for little more than a tavern that gangster John Dillinger used as a hideout in the 1930s. Even though I’ve visited this outcrop many times before, I drive past it on this autumn day and need to find a spot where three university vans can turn around. After managing to turn around and return from the other direction, we park on the shoulder. The students pile out of the vans, clearly unimpressed and confused as to why we’ve stopped here. They don’t yet realize that this is a hidden gateway to Earth’s interior.
I ask them to take a close look, kneel down for a few minutes, and use their magnifying glasses to observe what they find. Some grumbling follows – they’re getting hungry, and we’ve already seen plenty of rocks today – but they all comply. Within a minute, I hear exclamations of discovery: “Look at all that biotite!” and “So many tiny red garnets! What are those bluish crystals – kyanite?”
Their initial indifference fades into respect as they realize the rocks have undergone journeys no human ever could. We’ve discussed rocks like these in class – mica schists with their unlikely histories – how they act as messengers carrying stories from distant realms. But seeing them up close, in their current form, is a different experience.
Geologically, these rocks are considered ‘metamorphic’, meaning they were transformed by extreme heat and pressure deep beneath the Earth’s surface – and have somehow returned to the surface. Unlike igneous basalt, which forms from lava, or sedimentary sandstone, which is formed by water, metamorphic rocks are created in one environment and travel deep into the Earth’s crust. They are the ‘travel writers’ of the rock world, returning to share stories about the dynamic and hidden nature of our planet’s interior. With each stage of their journey, they preserve a record of their experiences, offering us a glimpse into subsurface worlds that humans may never directly encounter.