Join us Thursday, 10/22/26 from 6 - 7:30pm as John W. Jengo will give a free talk & book signing on The Geology of the Lewis & Clark Expedition in the Wagner’s lecture hall. Register here. This interview has been edited for clarity.

AC: Your book, Scenes of Visionary Enchantment: The Geology of the Lewis and Clark Expedition just came out this summer. Can you tell me a little bit about it?

JJ: The book is a multi-layered work combining historical interpretation and document analysis, evaluation of early American science in the Jeffersonian era, and episodic travelogue experiences along the acclaimed 8,000-mile-long Lewis and Clark Trail, which also includes pertinent vignettes from my professional environmental career. The book attempts to contextualize and assess the accuracy of the astonishing geological observations made by Captains Meriwether Lewis and William Clark during their 1804-1806 transcontinental expedition to the Pacific Ocean and back (including rock encounters along the Mississippi River when they were making their way upriver to encamp near St. Louis in the winter 1803-04). The book also covers my endeavors to locate all the extant rock, mineral, and fossil specimens that they collected (a search that extended from Philadelphia to Paris and included vertebrate fossils that helped fortify the emerging theory of species extinction), my own diagnostic testing of minerals along the Trail to ascertain the accuracy of the captains’ rock identifications, and my assessment of the lasting influences of this singular expedition on numerous nineteenth century explorers, geologists, and naturalists and the nascent mapping of the geology of the American West.

A thorough synopsis of the expedition is provided in addition to personal stories of my efforts to find the very same rock outcrops that the captains examined and to stand with certainty in the very same spots where the captains once stood. There are also interesting diversions about the various locales back East that Lewis and Clark referenced as they strived to draw comparisons and analogies to the spectacular features they were encountering, and pertinent digressions into art history, Native American oral histories and rock imagery, and the ecological/environmental best practices and remedies (e.g., dam removals) that I think will be necessary to restore the Trail and its river corridor to some semblance of its original grandeur.

“I think the captains’ geological observations have been hiding in plain sight to some degree”

AC: When in your research did you begin to take Lewis & Clark’s mineralogical collection and geological observations as significant, and where in their work do you find the gravity (or significance) that other expedition scholars have missed?

JJ: I started my own journey with Lewis and Clark when the 13-volume The Journals of the Lewis and Clark Expedition, edited by Professor Gary E. Moulton, was published by the University of Nebraska Press between 1983 to 2001. Throughout these journals, the captains’ remarks on the geology of the expedition route leapt off the page for me. But in reading the rich syllabus of Lewis and Clark secondary literature, there are comments from historians such as: “As Lewis and Clark moved on up the Missouri [River,] they had less and less to say about minerals,” because other matters “diverted their attention from such lackluster objects as coal, limestone, and lead ore” and “From the Great Divide to the Pacific their journal entries contain virtually no geological descriptions. Those which do appear are worthless.” With my background in geology (I received my B.S. and M.S. in geology in 1980 and 1982, respectively), I immediately knew this to be incorrect in many respects. For instance, after the expedition crossed the Bitterroot Mountains in Montana/Idaho, the geologic formations along the route radically changed to a landscape comprised primarily of volcanic basalt extending for hundreds of miles; thus, there literally weren’t any coal, limestone, and lead ore present to observe. That’s when I thought this subject needed to be further investigated.

I think the captains’ geological observations have been hiding in plain sight to some degree, and because these notations are a bit more nuanced than their exacting botanical and zoological morphological descriptions, other expedition scholars have rarely commented on the earth science aspects of the expedition journals and, in some cases, they heartily disparaged them. I thought perhaps I could place Lewis and Clark within the larger context of the geological sciences, particularly their influence on 19th-century American science. I hope readers and attendees will come away with a better appreciation for how perceptive Meriwether Lewis and William Clark were in recognizing geologic phenomena and admire how they managed to find the time to document the geology of the Expedition route, given the other enormous scientific responsibilities they had for recording their observations in botany, zoology, and ethnology, noting meteorological information, making astronomical observations, and producing accurate route maps

AC: To make an evaluative claim on the importance of Lewis & Clark’s discoveries requires a firm understanding of the state of science at the time of the expedition (1804-1806). Perspective on the history of science is one of the things the Wagner strives to provide the public—as we contain a free to attend, near-immaculately preserved Victorian natural history museum. What do you think the importance of understanding the history of science is when conducting research about past natural science discoveries and in creating new knowledge?

JJ: Comprehending the history of science is so very essential to understanding the main thesis of my book and how I recommend that we avoid a “presentism” view of the expedition’s geological observations (the practice of judging or interpreting historical figures and events using present-day standards and knowledge). Natural science in the early nineteenth century was dominated by a zeal for describing natural phenomena that were considered “fixed aspects of an essentially static world,” as opposed to attempting to ascertain the processes behind the formation of the natural world, which is how we generally conduct scientific research today. Thomas Jefferson, the visionary architect and sponsor of this enterprise, has been excoriated by some historians for not sending a true “scientist” to accompany the expedition but I vigorously defend the selection of Meriwether Lewis as the expedition’s chief naturalist. It did not require any particular training to be considered a scientist in this era, thus, it was more important to Jefferson to have a robust, courageous explorer ingrained with military discipline who could make detailed scientific observations rather than a more scientifically trained academic who was not likely to physically endure the journey. In advocating for a unbiased “historicism” view, which attempts to understand a historical figure or exploration on its own terms and within its original context, I concluded that it was the nascent state of the geological sciences when the expedition departed from the East in 1803, particularly the lack of an established mineral classification scheme or proven theories of geological processes, rather than deficiencies in the captains’ dedication or attention, that precluded a comprehensive evaluation of all the different rocks and minerals that the expedition encountered or the development of hypotheses about the immense geologic forces that formed the face of the West.

“Retracing the geology along the Trail has provided a more distinct and pronounced connection to the expedition for me.”

AC: The book is filled with spectacularly scenic photographs you’ve taken of the Lewis & Clark expedition trail. How has photographing the trail influenced your understanding of the expedition and their work?

JJ: I have found that photographing landscapes requires patience and multiple visits to the same locale. I can’t think of an instance when I wasn’t waiting for several hours for the perfect light to optimize the characteristics of the geologic formations that I photographed for the book. The front book cover is a representative example – I waited for over three hours for a momentary window of opportunity (which turned out to be only 30 seconds or so) when the setting sun emerged from overcast skies in the far distant western horizon and radiated a beam of warming light to illuminate the basalt cliffs at Crown Point in the Columbia River Gorge. I managed to compose five photos in the few fleeting seconds before the light was gone, one of which became the front cover. That time I spent waiting was used quite productively as it afforded me the opportunity to compose the shot and set up my tripod and then in the intervening hours, read both the captains’ journals from the day they encountered the same locale and the latest scientific technical papers describing the geology of the rock formations. When traveling, and I include myself in this category sometimes, we tend to rush from place to place, especially on a cross-country road trip following the Lewis and Clark Trail. But by settling at one location for hours on end waiting for the right photographic light, it slowed everything down for me so that I could fully appreciate the effort it took the expedition to reach this spot, I could ponder where Lewis and Clark stood to observe their surroundings, and it allow me to immerse myself in their words, find those features in the landscape, and for several ephemeral moments, imagine myself back in 1804-06.

AC: Over your nearly 30 years of following in the captains' footsteps, is there a moment on the trail that was most insightful, surprising, or is particularly vibrant in your memory?

JJ: There were many thrilling moments, and they occurred literally from the very beginning to the very end of my research area. To be able to track down a unique rock exposure that Meriwether Lewis noted on November 25, 1803, on the approach to Grand Tower (today’s Tower Rock) along the Mississippi River, all the way to crawling out over a dangerous precipice on Tillamook Head on the Pacific Coast to collect a white earth sample from where William Clark had taken a sample on January 7, 1806, and all the places in between. Retracing the geology along the Trail has provided a more distinct and pronounced connection to the expedition for me.

But I would say that the day I spent in the North Dakota badlands in Theodore Roosevelt National Park searching for pumice-like rocks that matched Meriwether Lewis’s April 14, 1805 journal entry – “while we remained at the entrance of the little Missouri, we saw several pieces of pumice stone floating down that stream” – was a memory that will never leave me. I had the park nearly to myself that late summer day. I spent hours crawling for hundreds of yards along the gently sloping riverbanks of the Little Missouri River (which probably looked odd had anyone been watching) collecting dozens of pumice-like rocks that had been stranded at higher elevations by more energetic river flows. These rocks are just a few inches long, distinguishable by their color (almost uniformly pink and reddish) and are characterized by tiny cavities called vesicles that give the rocks a very low density. When I placed a handful of these frothy rocks in the waters of the Little Missouri River, several of them easily remained buoyant and began to float confidently downstream. At that moment, I felt a deeply gratifying connection to Lewis and Clark and their pioneering scientific observations.