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 Geology of the northern Kenai PeninsulaThe rocks of the craggy peaks in the Kenai Mountains were born from sands and muds--at least a mile thick--deposited in an ancient sea about 65 million years ago. This material made up large alluvial fans at the western edge of North America. Carried offshore by ocean currents, the sand and muck settled to the sea floor.The tremendous weight of the sediment caused high pressures and temperatures that baked the muck, forming sandstone and siltstone. Hot silica-rich fluids, moving along faults in the stone, crystallized to milk-colored quartz veins after cooling. If nature was smiling, the fluids in the gold and silver became frozen in the veins. Over time, these veins weathered and released the gold into the streams. Quartz veins can be seen in road cuts on the west side of the Seward Highway, 2.7 miles north of Turnagain Pass. About 2 million years ago, climatic cooling and heavy precipitation caused the glaciers of the Kenai Peninsula to advance down valleys. Acting like bulldozers, the glaciers pushed the gravels and spread out the placer gold. A warmer trend about 12,000 years ago caused the glaciers to retreat. Glaciers left U-shaped valleys filled with surface gravels. Knells and ridges in the Turnagain Pass area were left by the glaciers that once filled the valley to a depth of at least 2,000 feet. Streams running off the glaciers eroded through the thick deposits of gravel containing placer gold. What remained were bench placers perched above present stream levels. Further erosion concentrated the gold-bearing gravel and redeposited the gold in gravel bars and backwaters of the newly formed stream channels. Most Kenai Peninsula gold has come from placers along Crow, Canyon, Resurrection, Lynx, Bear, Mills, Gulch, and Sixmile Creeks.
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