The geology of Alaska includes Precambrian igneous and metamorphic rocks formed in offshore terranes and added to the western margin of North America from the Paleozoic through modern times.
Until 200 million years ago, western North America terminated at the Rocky Mountains, 120 miles further inland than the current shoreline, until the addition of the Yukon-Tanana Terrane.
This intensely folded and rock unit extends from Fairbanks into the Yukon Territory in Canada and formed between 800 and 600 million years ago in the Proterozoic, due to the metamorphism of shale, sandstone and mudstone along the western margin of the continent.
A different schist belt may underlie the Brooks Range and is known from deep boreholes in the vicinity of Prudhoe Bay, reaching greenschist and blueschist on the sequence of metamorphic facies.
Volcanic rocks remain in the Keevy Peak Formation in the Northern Alaska Range and metamorphosed into the Totatlanika Schist in the interior, as well as in the Alexander terrane in the southeast.
[4] During the Cretaceous, tectonic activity in the Arctic Ocean created a series of sediment filled basins, which now host oil and gas deposits, underlying the continental shelf of northern Alaska.
[4] For much of the Cenozoic, Alaska experienced very cold conditions, preserved by fossils in the 5000 foot thick terrestrial sediments of the Chickaloon Formation in the Cook Inlet.
A steady supply of moisture from the Pacific Ocean supported coastal glaciers beginning five million years ago, recorded by the glacial mudstone of the Yakataga Formation along the Gulf of Alaska.
A return to cold conditions 3000 years ago in the Holocene brought major glacial advances in Glacier Bay and Icy Strait, reaching new maximums by 1750 before going into retreat.
Currently, Alaska is experiencing an ongoing terrane collision, with the uplift of the Saint Elias Mountains by the Yakutat Block, volcanism and deep granite formation.