Geological Field Guide · CO · OR · TX
Deep Time Terrain
The rock beneath your boots — what it was, when it formed, and what you can find.
Filter formations
Era legend
Proterozoic
1,800–1,000 Ma — ancient basement
1,800–1,000 Ma — ancient basement
Pennsylvanian–Permian
323–252 Ma — Ancestral Rockies
323–252 Ma — Ancestral Rockies
Jurassic
201–145 Ma — dinosaur floodplains
201–145 Ma — dinosaur floodplains
Cretaceous
145–66 Ma — interior seaway
145–66 Ma — interior seaway
Eocene
56–34 Ma — tropical calderas
56–34 Ma — tropical calderas
Miocene
23–5 Ma — flood basalts
23–5 Ma — flood basalts
Pliocene–Recent
5 Ma–now — active volcanics
5 Ma–now — active volcanics