Geologic timeline of Western North America

A timeline of significant geological events in the evolution of western North America. Dates are approximate. ("Ma" = millions of years ago)

Date Period/Epoch Event
350 Ma Devonian An unnamed terrane collides and accretes to the North American Plate, along a line roughly coinciding with the Nevada–Utah border and called the Carlin Unconformity.
250 Ma Permian The Sonomia Terrane collides and accretes to the North American Plate, along a line called the Golconda Thrust (also the name of the event) which runs through central Nevada.
200 Ma Triassic Sierra Nevada batholith first develops.
180 Ma Jurassic The Intermontane Plate collides with the Pacific Northwest, the remnants of which form the Intermontane Belt today.
165 Ma Jurassic The Smartville Block, an island arc terrane, collides and accretes to the North American Plate, along a line which coincides with the Mother Lode country of California.
140 Ma Jurassic Second wave of plutons added to Sierra batholith.
115 Ma Cretaceous The Insular Plate collides with the Pacific Northwest. The remnants of that terrane comprise the Insular Belt today, of which Vancouver Island is a part.
90 Ma Cretaceous Third and last wave of plutons added to Sierra batholith.
43 Ma Eocene The Pacific Plate changes its direction of motion from north to northwest.
35 Ma Eocene Rio Grande Rift begins to form.
20 Ma Miocene San Andreas Fault comes into being as the North American Plate begins splitting the Farallon Plate in two.
17 Ma - 14 Ma Miocene Columbia River Basalt Group Forms.
8 Ma Miocene Onset of faulting creating the Basin and Range geologic province.
5 Ma Miocene - Pliocene Northward propagation of the East Pacific Rise into the North American Plate initiates rifting off of the Baja California peninsula.
4 Ma Pliocene Sierra Nevada begins to rise.
3.5 Ma Pliocene The Pacific Plate changes its direction of motion about 11 degrees east of its previous heading, from northwest to the present northwest by north.
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