Composed of layered, coarse, brick red sandstone, dark red silt stone and conglomerate of the Fountain Formation, these huge monoliths are quite a site to see.    
The layers were deposited in torrential streams as debris washed off the east edge of the Ancestral Rocky Mountains ~ 300 million years ago.  As the Rocky Mountains were uplifted the monoliths were carve by erosion.

    A close study of the monoliths shows many eroded indentations.  The sandstone layers are more resistant to erosion then the silt stone layers, thus the sandstone layers tend to project out while the silt stone recedes.  This is a great example of differential erosion.

    On the west side of the parking lot there is a bronze plaque bolted to the rock about 10 feet above the ground.  This marks the boundary between the Fountain Formation and the much older rocks of the Idaho Springs Formation.  The Idaho Springs Formation are metamorphic rocks.  As you look at the contact between the two units, note the coarse gravel and pebbles at the base of the Fountain Formation.  These are composed of the same material as that of the metamorphic rock.  This unconformity spans a time interval of 1.5 billion years from the Precambrian Era to the Pennsylvanian Period.  This is on the the most widespread and longest periods of erosion the Earth has known next to the "Great Unconformity" in Scotland.

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