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North Cascades Geology

Geologic Time

spacer image Even geologists, who have opportunity to practice, have difficulty imagining the great length of time needed for geologic processes. We can think about a million years or even a billion years, but we can hardly imagine the countless small events that fill such expanses of time. And it is just such small events the settling of a sand grain to the ocean bottom, the tumbling of a rock off a thawing, north-facing mountainside, the death of a small snail that add up to geologic change.

Climber on the mountainside of geologic time
Climber on the mountainside of geologic time (climber not to scale).

Climbing a Mountain of Geologic Time

spacer image An ambitious hiker who climbs from Nooksack Falls, on the North Fork of the Nooksack River, to the top of Hadley Peak, crowning Chowder Ridge, north of Mount Baker, ascends about 5000 feet vertically about a mile straight up and climbs layered rocks of the Nooksack Formation spanning an age range of about 50 million years. Using this same scale, if our hardy hiker were to ascend the 400 million years of strata widely represented in the North Cascades National Park, he would have to climb vertically about eight miles. And if he were to climb metaphorically through strata representing the time encompassed by all the North Cascade rocks, including some that are about 1,600 million years old, he would have to climb about 32 miles straight up. In contrast, for the youngest episode of North Cascade history, the growth of the Mount Baker and Glacier Peak volcanoes in less than 1 million years, he would only have to scramble up about 100 metaphorical feet.

The Geologic Time Scale

spacer image Nineteenth-century geologists devised a time scale to represent the relative ages of rocks. The age of the Earth was then much debated, with estimates ranging from a biblical 6,000 years to figures on the order of 40 million years, still far short of the currently-accepted age of about 4.6 billion years. Despite disagreements as to the age of the earth, it was still possible in many places for everyone to agree that one layer of sedimentary rock rested on top of another and that the one on top was younger. As a result, geologists were able to create a relative geologic time scale based on such relationships.
spacer image No one knew the ages of rocks expressed in years until dating methods using naturally-occurring radioactivity were developed in the twentieth century. In this website we avoid using the plethora of relative geologic time terms (all those eras, systems, and epochs illustrated below). Instead, we give ages in years whenever possible, while reporting the relative ages in parentheses for those who enjoyed Jurassic Park and would like to know a little more about other time periods, such as the Triassic and Cretaceous.
Geologic time scale much simplified.

Geologic time scale much simplified. Click on events to learn more.

Dig deeper into Geologic Time

On to The Basic Pattern Emerges


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This site is a cooperative endeavor of the
US Geological Survey Western Earth Surface Processes Team
and the National Park Service.
Please share your comments and suggestions with us!
parkgeology@den.nps.gov

http://www.nature.nps.gov/grd/usgsnps/noca/nocageol3.html
This page was last updated on 11/30/99


Material in this site has been adapted from a new book, Geology of the North Cascades: A Mountain Mosaic by R. Tabor and R. Haugerud, of the USGS, with drawings by Anne Crowder. It is published by The Mountaineers, Seattle