GEOLOGICAL OBSERVATIONS BY LEWIS AND CLARK ALONG THE MISSOURI RIVER IN NEBRASKA IN 1804

The Lewis and Clark Corps of Discovery entered what was later to become Nebraska via the Missouri River on July 10th and left the state fully entering South Dakota on September 8th of 1804. William Clark's journal entries written during this period include observations on geologic features and phenomena that both he and Lewis had been charged by President Thomas Jefferson to record. On this leg of their journey their observations principally were on physiographic changes, fluvial and eolian processes, stratigraphy, paleontology, mineralogy, geologic hazards, and geomorphology. Clark noted that the grass covered plains commenced for the first time in southeasternmost Nebraska after the expedition had come through the largely tree covered areas of Missouri and northeast Kansas. The Missouri River was a meandering river with point bars, neck cutoffs, and oxbow lakes, some of recent vintage. In places remnants of older fluvial terraces were preserved along the valley sides of the Missouri. The Platte was a sandier and shallower river with more bars. The Niobrara, farther north, was similar to the Platte, but had more gravel in its bed load. Bars in the Missouri were unstable and eroded away rapidly at times. Their sands and silts were easily eroded and transported by winds. Sand dune and loess deposits resulted from the deposition of the sands and silts. Sandstones and limestones were common types of rock strata. The limestones often were composed of cemented shells. Lewis and Clark attempted to identify minerals in the rock strata using Richard Kirwan's book on mineralogy that they carried with them. Landslides, prairie fires, and other geologic hazards were reported. Erosional remnants of bedrock were often preserved in the form of buttes and conical hills along the valleys and on adjacent uplands. Examples of almost all of the geologic features and phenomena reported by Clark can still be seen today, mostly on public lands, in proximity to the places where they were originally described along particular reaches of the Missouri River more than 200 years ago.