A Fine Day for a Sail: Lewis and Clark on the Missouri

By editor

Roy, Fergus County, Montana

On May 24, 1805, Meriwether Lewis recorded in his journal a moment of calm navigation on the Missouri River: "We set out at an early hour this morning and proceed on principally by the chord untill about 9 A.M. when a fine breeze sprung up for the S.E. and enabled us though the ballance of the day to employ our sails to advantage." This brief note offers a glimpse into the daily progress of the Corps of Discovery as they journeyed through what is now central Montana, pushing ever westward toward the Rocky Mountains.

The river they sailed was a vital artery through a landscape both ancient and dramatic. The hills that framed their route on May 23, the day before Lewis’s entry, were described as "high and broken, a considerable portion of black rock and brown sandy rock appear in the faces of the hills… the whole producing but little grass." These hills are composed primarily of Bearpaw Shale, a formation laid down more than 70 million years ago during the Late Cretaceous period. This shale is a soft, gray, thinly layered sedimentary rock that was deposited on the floor of the Western Interior Seaway, a vast inland sea that stretched from the Arctic Ocean to the Gulf of Mexico, covering much of present-day Montana.

Imagine that ancient seascape: the water teeming with mosasaurs--formidable marine reptiles that could reach lengths of 50 feet--gliding alongside plesiosaurs with their long necks and paddle-like limbs, while ammonites, coiled shelled cephalopods, floated near the surface. On the shores, dinosaurs like the duck-billed hadrosaurs and armored ankylosaurs roamed, their footsteps eventually fossilized in the sediment. The early Rocky Mountains rose to the west, their volcanic peaks hurling ash that mingled with the sea sediments, contributing to the layers of rock that Lewis and Clark’s expedition would later pass.

The saline springs and bitter waters that troubled the expedition in this region owe their existence to these ancient marine deposits. As the Bearpaw Shale weathers, it releases salts that dissolve into the streams and groundwater. Lewis noted one such tributary’s water as "moderately pergative, but painfull to the intestens in it's operation," revealing the practical challenge of navigating a landscape whose geological history directly affected their health and survival.

This stretch of the Missouri River in 1805 was not the same riverbed we observe today. The river has meandered across its floodplain since the expedition’s passage, as all rivers with sufficient sediment and gentle gradients will. When Lewis and Clark sailed by, the river hugged the cut bank on the south side of the valley, carving a channel through the Bearpaw Shale and adjacent formations. Over the last two centuries, the river has shifted its course, leaving oxbow bends and abandoned channels etched into the landscape.

The geological processes shaping this region have unfolded over vast spans of time. The Bearpaw Shale formed approximately 75 to 70 million years ago, during a time when the Western Interior Seaway was one of the most extensive inland seas in Earth’s history. The gradual uplift of the Rocky Mountains, which began in the late Cretaceous and continued into the Cenozoic Era, exposed these marine sediments to erosion, sculpting the hills Lewis described as "high and broken." The valley through which the Missouri flows is a product of both this uplift and the relentless work of water cutting through the rock.

Lewis’s journal entries offer not only a navigational record but also keen observations of the terrain and its resources. His attention to detail reveals a mind attuned to the natural world and its challenges. The Corps of Discovery, composed of soldiers, frontiersmen, and naturalists, depended on such notes to understand the land and its potential for future settlement and commerce.

The river’s course itself was vital to their journey, providing the fastest means to traverse the rugged landscape. Sailing upstream against the current was laborious, but the arrival of favorable winds, as Lewis notes, allowed the men to hoist their sails and conserve their strength. The "fine breeze" from the southeast must have lifted their spirits as well as their boats, pushing them steadily toward the mountains that loomed ever larger on the horizon.

In addition to the physical geography, the expedition passed through lands inhabited by Native American peoples whose knowledge of the river and its resources was profound. While Lewis’s journals focus largely on the landscape and natural history, the human dimension of this voyage is inseparable from the environment. The Missouri River served as a highway for trade, communication, and sustenance long before European explorers arrived.

The subtle changes in the river’s course since 1805 provide a reminder of the dynamic nature of the landscape. Channels that once supported navigation have silted up or shifted, while new bends and bars have formed. This continual reshaping of the floodplain influences the distribution of plants and animals, as well as human use of the land. Today’s observers can compare modern maps with Lewis’s descriptions to appreciate how the river’s movements reflect ongoing geological and hydrological processes.

In reflecting on the expedition’s passage through this region, one recalls Lewis’s own words from May 24, 1805. The simplicity of his statement belies the complexity of the moment--a fine breeze, the use of sails, the movement through a landscape formed over millions of years. It is a reminder that exploration is as much about understanding the natural forces that shape a place as it is about charting new territory.

The Missouri River corridor near Roy, Fergus County, remains a site where the layers of time are visible to those who look closely. The Bearpaw Shale cliffs and the meandering river testify to ancient seas, rising mountains, and the ever-changing flow of water. Here, history and geology intersect, revealing the intricate story of a land that has long challenged and sustained those who travel its waters.

See also

• A Fine Day for a Sail at Roy, Fergus County
• Lewis and Clark National Historic Trail at Fort Benton, Chouteau County
• Evidence of the Expedition at Forsyth, Rosebud County