A Guide to the Geologic Sites Under the Big Sky

Available June 9, 2026

Robert C. Thomas

Illustrated by Chelsea M. Feeney

Every vista in Montana tells a geologic story, and in Montana Rocks! author Rob Thomas selects sixty of the very best geologic sites to reveal how the Big Sky state’s landscapes were built, reshaped, and transformed over time.

Each carefully chosen stop is a geologic time capsule, brought to life with beautiful photographs and clear, indispensable maps that shed light on crucial details. The sites are organized chronologically, inviting armchair readers and travelers alike to journey through the state’s geologic history from some of the world’s oldest rocks on the Beartooth Plateau to recent rockfalls in the state’s biggest city, Billings.

Sandwiched between the oldest and youngest sites are tales of ancient mountain building, fossil-rich limestone deposited in tropical seas, and torrential floods that drained ice age lakes. Glacier National Park, Montana’s crown jewel, boasts four highlighted sites, while others explore volcanic ash deposits carried north from Yellowstone’s colossal eruptions.

With this book in hand, readers will visit a nesting ground of dinosaurs, an earthquake-triggered landslide, crystal-bearing weathered granite, and thrust faults that carried entire mountains over younger rocks, bringing Montana’s long and complex geologic history into focus.

$28.00, paperback
160 pages, 9 x 8.375
ISBN 978-0-81374-127-7

Geological Society of America