Meet the Oldest Rock in the West

In this delightful piece for High Country News’ Deep Time in the West series, geosciences professor Marcia Bjornerud conducts “interviews” with 10 ancient rock formations in Wyoming—from the 3.5-billion-year-old Sacawee Gneiss to the Huckleberry Ridge Tuff that helped shape what is now Yellowstone National Park. “For 40 years, I’ve studied the language of rocks and found them to be wise mentors and matchless storytellers,” Bjornerud writes. This whimsical format offers humans a much-needed perspective on time, change, and our place in the world—if only we’d listen.

Great Unconformity: Frankly, I’m surprised you’re even interviewing me. Geologists generally treat me as a nonentity. I’m an un-rock, a cipher, just an irregular surface. But I’m actually pretty famous: People marvel at me in the Grand Canyon. It took a lot of patience to dismantle all that rock, erase mountains and become what I am. I feel like that merits respect.

MB: I think geologists do respect you, but you represent absence — negative space — and we’re not good at reading that.

Great Unconformity: I admit that I have some big gaps in my memory. What I do know is that sea level must have been pretty low in my time, because if it had been high, I would have been covered with water, and sediment would have collected instead of eroded.