Big Cottonwood Formation
​Age: Middle to Late Proterozoic from about 1 billion to 850 million years ago

The Big Cottonwood Formation consists of near shore marine sediments in the forms of shales and sandstones.  These sediments bear evidence of tidal action and daily tides can be identified.  It’s not an extensively studied rock strata but Marjorie Chan, of the University of Utah, has done some interesting work on these sediments.  By studying the rhythmic layering caused by tidal action, she has been able to study aspects of the lunar cycle almost a billion years ago.

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Large pebble of Big Cottonwood Formation sandstone showing rhythmic lamination of bedding