Stebbins Gulch Creek Bed

 

  Erosion surface on resistant creek bed

This is the view looking west down the stream towards the lip of the lower waterfalls in the middle background.  Here the creek is floored by an eight-inch-thick bed of siltstone that resists downward erosion. The flat surface runs for over 100 feet before ending abruptly at the lip of the lower waterfall. Large-scale topographic features often result from small differences in strength of the cement that binds the tiny grains that make up rock. For example, the shales that once covered the flat bed of siltstone have been eroded completely away. Shales are formed from compressed mud.  The clay minerals in the mud serve as a rather weak cementing agent, making the shale more vulnerable to chemical and physical weathering than the siltstone.  The tiny, hard quartz grains of the siltstone bed are cemented with amorphous silica, also a form of quartz. The result is a tougher layer of rock that forms the creek floor that also serves as the caprock of the waterfall downstream. 

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