Thousands of years in the past over the past Ice Age, rivers flowed from large glaciers within the Sierra Nevada right down to the Central Valley, carving into rock and gouging channels at a time when the ocean degree was about 400 ft decrease. When the glaciers retreated, meltwater coursed down and buried the river channels in sediment.
These channels left by historical rivers lie hidden beneath California’s Central Valley. Scientists name them paleovalleys, or incised valley fill deposits. As a lot as 100 ft deep and greater than a mile extensive in locations, they’re full of coarse-grained sand, gravel and cobbles.
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