Float down the Yukon River through Yukon-Charley Rivers National Preserve and you pass through more than 600 million years of Earth history. The river and its tributaries have cut through the rock to expose a relatively intact sequence reaching back to the close of the Precambrian — a record of rocks and fossils so complete it is considered of world significance.
The Charley River. Image from the National Park Service's Geologic Resources Inventory.
The preserve
Yukon-Charley Rivers lies about 175 km (110 miles) northeast of Fairbanks, on the Alaska–Canada border in east-central Alaska. It was established as Yukon-Charley National Monument on December 1, 1978, and redesignated a national preserve on December 2, 1980. It protects about 1,022,443 hectares (2,526,512 acres), including a 206 km (128-mile) stretch of the Yukon River and the entire basin of the Charley River. It also holds a rich collection of cultural sites from the 1898 Alaska gold rush and archeological remains of ancient Alaska Native peoples.
A collage of crust
The preserve sits in one of the most geologically active regions of North America. Its rocks are a collage of accreted terranes — pieces of crust added to the continent by plate tectonics, bounded by faults. The active Tintina Fault, a strike-slip fault running northwest to southeast, splits the preserve in two:
| Southwest of the fault | Northeast of the fault | |
|---|---|---|
| Rocks | Mostly Triassic to Cenozoic plutonic rocks, Mississippian to Late Triassic metamorphosed sedimentary rocks, and late Paleozoic metamorphic rocks | A more varied set of formations, from the Precambrian to the Pliocene |
| Oldest | The Precambrian Tindir Group, in the preserve's northeast corner |
Why it matters
- An unusually complete record. Diverse geological and paleontological resources spanning at least 600 million years.
- Undeformed crust. The area between the Nation, Kandik and Yukon rivers is thought to be a piece of the North American plate that escaped deformation, keeping an intact geological and fossil record. Some of the oldest known microfossils have been found here.
- Wild rivers. The entire Charley River watershed is protected in its undeveloped natural state and classified as a national wild river, and the Yukon is the largest natural, free-flowing river in the National Park System.
- Gold rush sites. Bucket dredges, mail trails, trappers' cabins, boats, roadhouses, water ditches and machinery preserve the region's gold rush history.
Mountains in the Tatonduk River drainage along the Canadian border. Credit: Josh Spice, National Park Service.
Maps and inventories
The Park Service's Geologic Resources Inventory, which produces digital geologic maps and reports for more than 270 natural resource parks, has published a geologic map of the preserve; its products are on the NPS DataStore.
Sources
Based on "NPS Geodiversity Atlas—Yukon-Charley Rivers National Preserve, Alaska," National Park Service Geologic Resources Inventory, which cites National Park Service (2016); a work of the United States government in the public domain.
In these publicationsYukon - Charley Rivers National Preserve
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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