Mineral Encounters in NE Nebraska

Tall, eroded river bank with layer of dark earth

Ionia Volcano

Photo © John Jengo

Ionia Volcano, an exposed bluff of Carlile Shale that includes a selenite-rich outcrop of "blue earth," is located approximately 3. 5 miles northeast of Newcastle, Nebraska. Cartographic reconstructions have concluded that the Missouri River was not undercutting this bluff when the expedition passed through on August 22, 1804 and neither the captains nor the other journal keepers had taken note of any volcanic occurrences in this area, indicating that the Ionia Volcano was not the subject of the captain's subsequent bluffs "on fire" observations.

masthead saying 'We Proceeded On'
Reprinted from We Proceeded On1

For every Lewis and Clark scholar, aficionado, or casual trail traveler, there are portions of the Lewis and Clark Trail that hold a special meaning, where connections can be made to the captains, the enlisted men, the native cultures, the flora and fauna, or the landscapes that were so vibrantly memorialized in the expedition journals. Those whose interest lies in the earth science aspects of the expedition can readily retrace certain sections of the Trail by tracking down the geological features that Lewis and Clark visited, experienced, and described.

Among the most compelling regions are the bluffs of northeastern Nebraska from southeast of present-day Ponca State Park leading northwestward up to the Calumet Bluffs. It was along this extraordinary stretch of river and terrain, which the expedition traversed between August 22 and September 1, 1804 (a distance of approximately 95 river miles according to Clark's figures), that the most intensive mineral collecting took place.2

As a consequence of the Missouri River running close to the base of the bluffs in strategic areas, rock formations were revealed to the explorers that were geologically diverse, distinctly colored, rich in mineral content, and in some places, dramatically distinguished by steaming and smoking hot earth that beckoned to be investigated.

  • 1. John W. Jengo, "'Blue Earth,' 'Clift of White' and 'Burning Bluffs'," We Proceeded On, Volume 37, No. 1 (February 2011), the quarterly journal of the Lewis and Clark Trail Heritage Foundation. Editorial additions include page titles, side headings, and graphics to assist the web-based reader. The original printed format is provided at http://lewisandclark.org/wpo/pdf/vol37no1.pdf#page=8.
  • 2. Some 49% of the 47 minerals that have documented collection dates were obtained in this short time period, making it by far the most productive sampling phase of the expedition.