Between 170 and 40 million years ago, western North America experienced a mountain-building period called the Sevier orogeny. Dense oceanic crust beneath the Pacific Ocean collided with and moved under the lighter continental crust of North America.

This convergence generated compressional forces that produced low-angle thrust faults within the crust. Transported tens of miles eastward along these thrust faults, rock formations were pushed up and over adjacent rock layers, forming the Sevier mountain belt.
The conglomerate of the Henefer Formation was deposited about 90 to 85 million years ago when Sevier thrust faulting in Utah had reached its peak. The conglomerate is composed of sandstone and quartzite pebbles, cobbles, and boulders eroded from the mountainous areas to the west and northwest. Streams then carried these sediments off of the highlands, eventually depositing the heavier material in large alluvial fans (fan-shaped stream and debris-flow deposits).
In more recent times, the elements have eroded areas of the conglomerate near Echo and within Echo Canyon into the fantastic shapes we see today; in addition to The Witches, there are rock structures named Pulpit Rock, Castle Rock, Devils War Club, Sphinx, and Sentinel Rock, to name a few.

The upper “caps,” or witches’ hats, are formed of a lighter-colored conglomerate layer cemented into a harder mass than the softer, underlying conglomerate layer that forms the witches’ “robes.” The harder cap rock erodes more slowly and helps protect the rock underneath.

But as a witch becomes more and more slender, her hat eventually falls off and can no longer protect her, and thus, like the infamous Wicked Witch of the West, she succumbs to the effects of water and gradually melts to the level of the surrounding landscape.

From the Utah Geological Survey

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