Yukon - Charley Rivers National Preserve - Faults

Millions of years ago, two crustal plates shifted along the Tintina Fault causing super-heated water to carry readily soluble mineral, including gold and silica, toward the surface. As the water cooled in a myriad of cracks formed in the fault zone, silica precipitated out forming quartz. Impurities such as gold trapped in the quartz concentrated as well. Pockets of gold existed in the rock around the fault zone until erosional forces tore the gold from the quartz" grip and sent it tumbling down mountain streams. As the gold churned with other rocks it gradually settled to the bottom. Placer mining has been the method used for recovering this gold since prior to the Klondike Gold Rush.

The Tintina Fault divides the preserve into two distinct geologic areas. The Tintina Fault is a strike-slip fault that runs parallel to the Yukon River corridor six to twelve miles south of the river. This fault is one of the great fault systems in western North America, extending 600 miles from northeastern British Columbia into Alaska.

Northeast of the Tintina Fault, the greatest bedrock diversity occurs in a triangle formed by the Nation and Yukon Rivers and the Canadian border. This triangular area is the only portion of east-central Alaska thought to be part of the original North American plate and it comprises a sequence of unmetamorphosed sediments (Precambrian, Cambrian, Ordovician, Silurian, Devonian, and Mississippian periods). These sedimentary rocks were once part of a continental margin and contain an outstanding record of marine faunal evolution that includes ammonites, trilobites, brachiopods, and corals. The oldest known microfossils from northwestern North America are also found in this triangular area. The area southwest of the Tintina Fault is a sequence of complex igneous, metamorphic, sedimentary and volcanic rocks. These were probably metamorphosed and reformed when several small plates collided to form Alaska during the Cretaceous period.