CONSTRUCTING OREGON
The rock units and ages shown on this map tell a simplified story of the geologic history of Oregon. The units were assembled from the Oregon Geologic Data Compilation, a new digital geologic map of Oregon completed in 2009. The new map was made possible by digitizing 345 geologic maps with thousands of different geologic units and arranging the rock units by type and age. Having all of Oregon’s geology in one digital map makes it possible to organize rocks across the state into the major geologic layers that together have built the Oregon we see today. Each layer results from a major geologic event — some long-lived, some a geologic instant — that assembled the state like a complex building. With these layers, we can think of three phases of construction:
PHASE 1
FOUNDATION — Rocks many miles thick underlie the entire state and range from 400 million to 50 million years old.
Generalized Geologic Units:
- Exotic Terranes: foundation blocks of Oregon
- Batholiths and Plutons: mortar for the foundation
- Early Sediments: Oregon’s first coast
PHASE 2
BRICKS AND MORTAR — Volcanic and sedimentary rocks thousands of feet thick cover most of the foundation. These rocks are generally between 60 million and 2 million years old.
Generalized Geologic Units:
- Siletz Terrane: last exotic arrival
- Early Volcanic Arc: Oregon’s tropical volcanoes
- Coast Range Sediments: 50 million years of mud
- Coast Range Volcanoes: Oregon’s first hot spot
- Columbia River Basalt: the Yellowstone hot spot arrives in a flood of fire
- Rift Volcanoes: aftermath of the Yellowstone hot spot
PHASE 3
PLASTER AND PAINT — This is the familiar land that we live on. Rocks hundreds of feet thick began forming 15 million years ago and continue to be shaped today.
Generalized Geologic Units:
- Ancient Waterways: home of Oregon's first salmon
- Rattlesnake Tuff: Oregon’s largest known eruption
- High Cascade Volcanoes: land of fire and ice
- High Desert Volcanoes: sleeping giants of eastern Oregon
- Lakes, Rivers, and Dunes: painting the landscape
- Pluvial Lakes: Oregon’s inland seas
- Glacial Deposits: runaway global cooling
- Ice Age Floods: Oregon's best soils lifted from eastern Washington
- Mazama Deposits: a jewel born of destruction
- Unstable Oregon: land of 10,000 landslides
- Cascadia Subduction Zone Earthquakes: the big one(s)
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