Geologic Time Scale
Follow the links below, in Epochs, Periods and Eons, to brief lists of important geological events in the Pacific Northwest.
(Note: In recent years an international group of geologists has cobbled together a revised geologic time scale in which the Tertiary and Quaternary Periods have been replaced by the Paleogene and Neogene Epochs. In the revised geologic time scale the Paleogene Period contains the Paleocene, Eocene, and Oligocene epochs and the Neogene Period contains the Miocene, Pliocene, Pleistocene, and Holocene epochs. However, until the revised geologic timescale is finalized, which is currently projected to be in the year 2008, we will keep using the Tertiary and Quaternary periods as listed below.)
| EON | ERA | PERIOD | EPOCH |
|---|---|---|---|
| Phanerozoic 544 Ma - present |
Cenozoic 65 Ma - present |
Quaternary 2 Ma - present |
Holocene 10,000 years ago - present |
| Pleistocene 2 million - 10,000 years ago |
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| Tertiary 65-2 Ma |
Pliocene 5.3-2 Ma |
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| Miocene 23.8-5.3 Ma |
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| Oligocene 33.7-23.5 Ma |
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| Eocene 55.5-33.7 Ma |
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| Paleocene 65-55.5 Ma |
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| Mesozoic 248-65 Ma |
Cretaceous 145-65 Ma |
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| Jurassic 213-145 Ma |
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| Triassic 248-213 Ma |
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| Paleozoic 544-248 Ma |
Permian 286-248 Ma |
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| Pennsylvanian 326-286 Ma |
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| Mississippian 360-325 Ma |
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| Devonian 41-360 Ma |
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| Silurian 440-410 Ma |
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| Ordovician 505-440 Ma |
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| Cambrian 544-505 Ma |
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| Proterozoic 2.5 billion - 544 Ma |
Precambrian | ||
| Archean ~3.9-2.5 Ga | |||
Holocene epoch
- Mastodons and woolly mammoths become extinct early in Holocene
- Sea level rises rapidly as continental glaciers finish melting
- Coastal erosion and deposition forms new shorelines, beaches, and sand spits
- Streams establish new flood plain levels, deltas, alluvial fans
- Devastating subduction earthquakes and tsunamis on coast every 200-1,000 years
- Earthquake on Seattle fault produces Puget Sound tsunami, landslides
- Alpine glaciers advance during Little Ice Age (130-800 BP), retreat since then
Pleistocene epoch
- Modern composite cones of Cascade Range begin
- Yellowstone caldera forms in cataclysmic eruption
- Continental ice sheets form in Canada and advance into northern US
- Sea level drops as much as 400 ft as water is sequestered in glaciers
- Alpine glaciers grow larger and merge locally into ice caps
- Cooler, wetter climate creates large lakes in basins of the Basin and Range
- Glacial Lake Missoula floods create Channeled Scablands at end of Pleistocene
- Ocean water enters Puget Sound at end of Pleistocene
Pliocene epoch
- Yakima Fold Belt continues folding and thrust faulting
- Course of Columbia River adjusts to Yakima Fold Belt uplift
- Thick layer of gravel shed by erosion of Rocky Mountains
Miocene epoch
- Columbia River Basalts erupt
- Yellowstone hot spot eruptions begin
- Basin and Range region begins forming
- Yakima Fold Belt begins developing
- Columbia Plateau region moister, more forested
- Relative of rhinoceros among animals in Columbia Plateau region
Oligocene epoch
- Sediments accumulate in coastal bays and estuaries east of present-day Pacific shoreline
- Western Cascades of Oregon die down, High Cascades start up
- Cascade Volcanic Arc in Washington starts up
- John Day Formation ash and sediments accumulate in eastern Oregon
- Early relatives of modern horse in eastern Oregon
Eocene epoch
- Puget Group sandstones and coal beds accumulate
- Palm trees grow in what is now western Washington
- Chiwaukum graben forms and fills with clastic sediment
- Republic graben forms and fills with volcanic rocks and volcaniclastic sediment
- Metamorphic core complexes form
- Straight Creek Fault undergoes extensive strike-slip motion
- Alkalic intrusions and alkalic volcanic eruptions in central Montana
- First terranes of the modern Coast Ranges begin accreting
Paleocene epoch
- Last of the inland seas deposits sand and coal in Montana and Wyoming
- Terranes of the North Cascades and British Columbia Coast Range move northward
Cretaceous period
- Period ends with large meteorite impact, demise of last dinosaur species
- Shallow inland ocean transgresses east of Rocky Mountains to the point that Arctic Ocean connects with Gulf of Mexico
- Laramide orogeny uplifts large blocks of continental basement
- Sevier orogeny folds and thrust faults the upper crust
- North Cascades-British Columbia Coast Range orogeny intrudes and metamorphoses
- Large-volume intrusions form batholiths in North Cascades, British Columbia Coast Range, Okanogan Highlands, and Idaho
- Insular Superterrane, including Wrangellia, accretes
- Terranes of western North Cascades and San Juan Islands accrete
- Blue Mountains terranes accrete
Jurassic period
- Intermontane Superterrane accretes to North America
- Kootenay Arc of northeastern Washington undergoes folding and intrusion
- Transgression of inland sea forms Sundance Sea east of early Rocky Mountains uplift, leading to widespread limestone deposits
- Early uplift of Rocky Mountains region occurs
- Convergent plate boundary with subduction zone becomes established in Pacific Northwest
- Pangaea finishes rifting into separate continents
Triassic period
- Pangaea begins rifting into separate continents
- Deserts with sand dunes widespread in Rocky Mountain region
- Several terranes that later accrete to North America exist in Tethyan area
- Single world ocean with a single large bay in Pangaea-the Tethys Sea
- Huge Pangaea landmass affects climate, causing widespread aridity
Permian period
- Pangaea finishes colliding and assembling
- Shallow seas cover parts of Rocky Mountain region
Pennsylvanian period
- Antler orogeny ends early in Pennsylvanian period
Mississippian period
- Lime deposits accumulate from sea-dwelling organisms on broad, flat continental shelf from Arizona to Canada, forming thick limestone sequence
- Antler orogeny reaches its peak
Devonian period
- Antler orogeny begins in parts of Nevada and southern Idaho
- Passive continental margin accumulates sediment layers in Rocky Mountain region
Silurian period
- Passive continental margin accumulates sediment layers in Rocky Mountain region
Ordovician period
- Passive continental margin accumulates sediment layers in Rocky Mountain region
Cambrian period
- Ocean transgresses across much of interior and western North America, depositing sand, then mud, then lime as water gets deeper
Proterozoic eon
- Ice age occurs near end of Proterozoic
- Continent rifts apart in Idaho-eastern Washington; the portion to the west drifts away with moving plates
- Deep rocks of Belt Basin undergo metamorphism
- Purcell Sill and other mafic intrusions occur in Belt Basin area
- Belt Basin accumulates mud, sand, and lime in wide, saline lake or broad ocean bay
Archean eon
- After erosion, shallow ocean transgresses continental platform and thin layers of sedimentary deposits accumulate
- Stillwater Complex intrudes in Montana
- New continental crust forms in Rocky Mountain region by tectonic compression, terrane accretion, intrusion, and metamorphism
Geology of the Pacific Northwest
Focus Page #2--Geologic Timeline of the Pacific Northwest
© 2001 Ralph L. Dawes, Ph.D. and Cheryl D. Dawes
updated: 09/28/06
Focus Page #2--Geologic Timeline of the Pacific Northwest
© 2001 Ralph L. Dawes, Ph.D. and Cheryl D. Dawes
updated: 09/28/06