Big Bend National Park's Mule Ears. We know many travelers like to keep one of William MacLeod's books open while they drive through the region, including:
Big Bend Vistas: A Geologic Exploration of the Big Bend
River Road Vistas
Davis Mountains Vistas
MacLeod's books offer a detailed explanation of the geology of the scenery from the road, making it easy for the traveler to understand (in depth, if the traveler wants) how and why the land looks as it does today. Don't know geological terms? There's a glossary in the back of each book.
Included in Big Bend Vistas: A Geologic Exploration of the Big Bend, is an entire section on Ross Maxwell Scenic Drive, where we learn the spiky Mule Ears formation is magma that solidified before it reached the surface, and over time, erosion revealed the "ears." The park's website's page on Ross Maxwell Drive also provides information on where you can stop along the road and proceed on trails to explore by foot.
To learn more, here's Big Bend National Park's website's page on the geology of the park.