Great Plains Geology

Abstract

Great Plains Geology is one of two books published so far in the Discover the Great Plains Series; the other isGreat Plains Indians by David J.Wishart. Robert Diffendal’s intended audience for the book is “anyone with a broad interest in geology and some general education in science, professional geologists and geographers wanting to become more familiar with the region, and students, farmers, ranchers, and K-12 educators who want to know about the Great Plains and its geological development.” While archaeologists are not listed among those for whom the book is targeted, Diffendal does provide some geological context for a few important Paleoindian sites in the Great Plains. Diffendal has divided his book into three main sections after the Introduction. His Introduction contains a full-color geological time scale with major Earth impacts by asteroids, times of large extinctions, and glaciations noted on the scale. The time scale is his background for discussing the evolution of the Great Plains in Chapter 2 and rock formations at 57 sites across the Great Plains from Alberta, Canada to southwestern Texas in Chapter 3. His introduction also includes a discussion of more than 50 geographic definitions of the Great Plains. In Chapter 1, “What is the Great Plains” (12 pages), Diffendal argues for his own boundaries of the Great Plains while generally following Charles B. Hunt’s (1974) definition of physiographic regions. Diffendal uses “uplift, earthquake faulting, bending and folding of rock layers, volcanism, or a combination of these processes” to define his 10 sections of the Great Plains. Two of his 10 sections are subdivided. One subdivision is based on glaciated versus unglaciated, and the other on abrupt, yet small in areal extent, uplift of hills (Cypress Hills of Alberta). Chapter 2, “Geologic History of the Great Plains” (20 pages), addresses tectonics, sea-level changes, glaciation, and accompanying drainage changes in the Great Plains. Chapter 2 is a succinct introduction to the geologic development of the Great Plains. Diffendal graphically outlines, at two times during the Upper Cretaceous Period, the area of the Western Interior Seaway that stretched from the Arctic Ocean to the Gulf of Mexico. This provides a large part of his background for the sedimentary rocks found in the Great Plains. Chapter 3 ofGreat Plains Geology, “Visiting the Great Plains”, highlights 57 sites that illustrate the geology and development of the Great Plains. Some are national parks, more are national monuments, and some are state parks or recreation areas. Very few are on private land, so most are readily accessible by the public. Diffendal labels each of the 57 sites with one of more of the following features: geological, paleontological, archaeological, and ecotourism. Interestingly, the first and last sites of Diffendal’s survey of locations in the Great Plains are archaeological sites. He begins his discussion with the Head Smashed-In Buffalo Jump site in Alberta, Canada, his most western site. He ends the chapter with a discussion of the Middle Archaic Fate Bell Shelter in Seminole Canyon State Park, southern Texas, along a tributary to the Rio Grande. Between these two sites you will enjoy reading about the geology of fourteen other archaeological and historical sites. While sixteen of the 57 sites listed by Diffendal in his book are classified as archaeological sites, four would be more accurately labeled as historical sites (Pompeii’s Pillar National plains anthropologist, Vol. 65 No. 255, August 2020, 274–279