16
LEWIS AND CLARK AND
THE GEOLOGY OF THE GREAT PLAINS
ABSTRACT
R. F. Diffendal, Jr., Conservation and
Survey Division, University of Nebraska
and Anne P. Diffendal, Historian
Meriwether Lewis and William Clark undertook their journey in 1804-06 in order to explore the area, known as
Louisiana Territory, which the United States had purchased from France in 1803.
In his written instructions to Lewis, President Thomas Jefferson charged the expedition principally to follow
the Missouri River to its headwaters and then locate rivers flowing down the west side of the Rockies to the
Columbia River and into the Pacific, in order to find the best route across the continent. Jefferson further
specified that they collect and describe plants and animals new to science; record the latitude and longitude of
the rivers, mountains and other features; to note the land's potential -- its farming lands, climate, water supply,
timber, wildlife and mineral resources. Their journals, notebooks and maps indicate that they took this charge
to heart and compiled a great deal of information on these topics.
Lewis and Clark were astute observers of the land through which they traveled. In most cases, however, they
did not know what had caused its appearance. At that time, few, if any, would have because the discipline of
geology was in its infancy. James Hutton, the father of modern geology, had published his Theory of the Earth
with Proofs and Illustrations in 1795 but few people were aware of the work nine years later. The concepts of
geologic time and of absolute dating were only beginning to be developed in Europe. The first geologic map--
that by William Smith in England-- was not published until 1815. The ideas of continental glaciation and re-
peated widespread flooding of the continents by oceans had not yet been proposed.
However, some people did know, at least in a general way, something about geology including how to identify
minerals. They recognized fossils. They were also aware of natural hazards such as landslides, floods and vol-
canic activity. From the notations in their journals, it is clear that both Lewis and Clark understood these as-
pects of geology. Among the books that they took with them was Richard Kirwan's Elements of Mineralogy,
published in London in 1784.
While Lewis and Clark frequently described geologic features, they seldom speculated on the processes that
might have produced them. The few exceptions deal mostly with the effects of flowing water. They noted
banks being undercut and landslides, as well as shifting sand bars and old river channels and cut-offs. They
also commented on water's role in rounding pebbles and in shaping rock.
Today we will take you on a journey up the Missouri River from the Kansas-Nebraska border to the mountain
front in Montana and back down the Yellowstone River in Montana to see some of the geologic features de-
scribed by Lewis and Clark. We have selected features that are accessible to today's traveler either located on
public land or visible from public land or along roadways.
The Diffendals will be here to give this talk on Thursday, September 25th
Bank of America Auditorium
12:30 PM
SCIENTIFIC COMMUNICATIONS