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Hoodoo in Late Cretaceous sandstone

(click for a larger version)
Jacob Thacker

— November 29, 2021

Hoodoos are gravity defying testaments of weathering and erosion. This small hoodoo (note the 14 inch long mapboard for scale) in sandstones of the Crevasse Canyon Formation near Gallup showcases how these features form. The upper dark brown sandstone is much harder and more resistant to erosion than the "friable" (easily eroded and crumbling) light tan sandstone beneath it. Being more resistant to the elements, the dark brown rock erodes much more slowly, while the light tan sandstone beneath it erodes much more quickly. This contrast in erodibility leaves a large cap rock over a small pinnacle.

The rocks in this photo also exhibit crossbedding, shown by the layers that angle down to the right of the photo within the dark brown strata (crossbeds are also in the tan sandstone but not as easily identifiable). The approximately flat line separating the brown sandstone from the tan sandstone is the bedding plane (the surface that separates two distinct stratified layers of rock). Crossbeds can be used to tell us what way wind or water was flowing when a rock was deposited, a crucial first step in determining bygone environments and topography on Earth.

Classic examples of hoodoos can be found all over the American Southwest, such as in Bryce Canyon National Park in Utah and at numerous national parks and public lands here in New Mexico. Please note: these features are fragile, so be sure to appreciate their odd beauty from a safe distance rather than on top.

— Jacob Thacker, Field Geologist