Great Plains Geology | Prairie Public Broadcasting

Great Plains Geology

Jul 15, 2019

Great Plains Geology, by R. F. Diffendal Jr., is a recent volume in the Discover the Great Plains Series of handbooks organized out of the Center for Great Plains Studies, University of Nebraska, and published by University of Nebraska Press. The author is professor emeritus of geology, UNL, and has a strong record of writing for academic and popular audiences.

The first chapter addresses the question, “What Is the Great Plains,” and offers a definition based strictly on geology. This excludes many localities commonly considered to be within spatial definitions of the Great Plains, including that done by the Center for Great Plains Studies itself--but that’s OK.

The author then provides a geologic history of the region, beginning with definitions of concepts (horizonality, superposition, and so on) and then discussing formative and transformative forces through time (climate change, deposition, glaciation, erosion, and so on).

Then the bulk of the book tours selected sites in the provinces and states of the Great Plains, beginning with Head-Smashed-In Buffalo Jump, Alberta, right through to Seminole Canyon, Texas.

The author loves certain sites and waxes lyric about them. Ashfall Fossil Beds, for instance, a state park in Nebraska, exhibit a wondrous array of Miocene mammal fossils including horses, camels, deer, dogs, and a rhinoceros. Diffendal writes:

How serendipitous were the geologic events that led to this wonderful site being preserved for us to see? Let us consider. A supervolcano, located on today’s Snake River Plain in Idaho, shot volcanic ash high into the atmosphere. It then happened to be carried eastward to northern Nebraska by favorable winds. Herds of Miocene mammals and groups of other animals happened to be in the area of a waterhole on the plains when the ash began to fall. The animals died and were quickly covered by more ash. The mid-Pliocene ancestral Platte River did not deepen its valley . . . and erode away the fossil-bearing beds. The western edge of the Pleistocene ice sheet stopped a few miles short of moving this far west and destroying the fossils.

This is great public science writing! I wish all the fifty-seven entries were as engaging, but many are not.

North Dakota, unfortunately, gets short shrift. Diffendal excludes most of the state from his definition of the Great Plains and only describes Theodore Roosevelt National Park as well as, for reasons unclear to me, Fort Union. Killdeer Mountain, Knife River Flint Quarries, the spectacular buttes of the West River--not included.

Standard works in the history and practice of geology in other plains states--North Dakota, Kansas, South Dakota--oddly absent from the bibliography.

Near the end Diffendal asks the question, “Is there any evidence on the Great Plains related to the end of the Age of Dinosaurs?” The answer given is, to paraphrase, not so much. Not long after publication came word that University of Kansas paleontologist Douglas Preston, working in Bowman County, North Dakota, had unearthed the world’s best-defined known fossil evidence of the close of the so-called Dinosaur Age via asteroid strike. Well, this is no discredit to the author or publisher of Great Plains Geology. It's just evidence that knowledge, like life, generally creeps along, but now and then an asteroid strikes.

Buy the book, Great Plains Geology, to carry in your cubbyhole as you travel the plains--but stock some other handbooks, too.

~Tom Isern

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