Yukon-Charley Rivers National Preserve is one of the rare locations in North America where so much of geologic history is preserved (Precambrian era to the Cenozoic). The Yukon River meanders through the preserve for a distance of approximately 130 river miles and drops about 200 feet along its route. The Yukon River and its tributaries cut rough-hewn cliffs, exposing remarkably complete records of the floral and faunal history of Eastcentral Alaska.
Since less than five percent of the preserve was ever glaciated, most of the geologic and paleontologic records are not buried under glacial debris. Glaciers that did form were not broad ice sheets, but alpine glaciers formed only in the highest portions of the Charley and Seventymile river drainages.