The caprock for this waterfall is a 9-inch-thick layer of fine-grained sandstone. It occurs about half-way up the Gulch in the Bedford Formation. The Bedford unit overlies the Cleveland Shale we encountered down the creek. It contains many thin beds of siltstone and sandstone, resulting in a sudden increase in step-like waterfalls and cascades as we move into the middle portion of Stebbins Run. They all work on the same principle, migrating upstream one broken piece of siltstone at a time as the underlying shale layer erodes away. Their more famous cousin, Niagara Falls, behaves in exactly the same way. The only difference is that Niagara occurs in older, Silurian-age rock, and its caprock consists of hard dolomite, a relative of limestone high in magnesium. But its caprock is also underlain by weak shale, so that Niagara Falls slowly migrates up the Niagara River, having regressed seven miles in 12,000 years.
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