Eagle Formation, Billings Montana

One of my favorite places to hike in the Billings area is Zimmerman Park, which is mostly atop the Rimrocks, a cliff formed by sandstone of the Cretaceous Eagle Formation. The Eagle Formation is usually interpreted to be either a barrier island deposit, similar to Padre Island in Texas, or a shallow marine sand bar that ran parallel to the shoreline. The sand was deposited in the Western Interior Seaway, a shallow body of water which stretched across North America from the Arctic to Gulf of Mexico. From Billings, sedimentary rocks become increasingly marine-dominated to the east, and terrestrial to the west.

USGS. From http://en.wikipedia.org/wiki/File:Cretaceous_seaway.png
USGS. From http://en.wikipedia.org/wiki/File:Cretaceous_seaway.png

Here are a few pictures from today’s late afternoon hike:

Sacrifice Cliff (Eagle Formation), east of downtown Billings. The top of the cliff is about 500 feet above the base of the talus slope. Crow Indian legends state that men (the number varies depending on the version of the legend) jumped off the cliff during a smallpox outbreak.
Eagle Formation from above Zimmerman Trail.
Ponderosa pine saplings growing out of a fracture on top of a bedding plane.
Ponderosa pine saplings growing out of a fracture.
Concretions (iron-
Concretions weathering out of the sandstone.  Concretions are post-depositional features formed when cement (in this case iron oxides) accumulates around some sort of nucleus. The concretions are then more resistant to erosion than the surrounding sandstone. The Earth Science Picture of the Day has featured concretions from the Eagle Formation.
Me standing next to a concretion.
Me standing next to a concretion.
Concretions and weathering.
Concretions and weathering.
Sunset over the Yellowstone River valley.
Sunset over the Yellowstone River valley.


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