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Thinking Geography: How the Decision at the Marias Was Made

By: Phil Scriver, LC200 Historian

“We came to on the Lard side in a handsome bottom of small cottonwood timber opposite to the entrance of a very considerable river, but it being too late to examine these rivers minutely tonight we determined to remain here until morning.” From Lewis’ journal entry for June 2, 1805. They had just encountered a large river the Indians at Mandan had not told them about. To the Captains this was “astonishing” since the rest of their geography had been very reliable.

The Captains’ journal entries for the next seven days give a great insight of their knowledge of geography—that is being able to look at the landscape presented and “read” or understand what they were seeing. We also get a chance to see just how these men thought; how they took facts and arranged them to formulate a logical conclusion. Although initial inspection gave some facts the Captains would not allow themselves to be completely convinced of the resulting conclusion until a greater body of information (facts) could be accumulated. Thus we see the first characteristic of their logical thinking was that they wanted all the facts possible before reaching a final conclusion. We find from reading these entries that they worked from the simple to the complex. And we find that they fully understood how important their decision was “to mistake the stream would not only lose us the whole of this season (of traveling) but would probably dishearten the party that it might defeat the Expedition altogether.”

They sent a canoe and three men up each river and several land parties out on one-day trips to try to see if they could discover the course of each river into the distance. The Captains climbed a hill on the point between the two rivers to examine the country. From this point the Captains saw “the country around us in every direction was one vast plain.” Visible in the distance were a series of mountain ranges to the south and southeast. When “both river channels soon became lost from view in a common plain” they realized the simple approach of climbing a hill and looking around would not give the answers they needed.

Now they would examine each river to see what could be learned. The South River was 372 yards wide with perfectly transparent water, fast water with a smooth surface, and a bottom made of round flat smooth stones “like most rivers issuing from a mountainous country.” The North River was 200 yards wide with a slower current, but a deeper channel. In this river the water was very thick and turbid and ran in the same boiling and rolling manner with the same whitish-brown color that characterized the Missouri River below this fork. In short the character of the North River was precisely like the Missouri they had been traveling. The Captains concluded from this inspection that the North River starts in and passes a great distance through the open plain. Therefore, instead of starting in or running to the mountains, it went north staying in the plains. If it went into the mountains it would have clearer water.

The parties that had been sent out in canoes and overland had gone about ten miles, they returned with no additional information. The Captains decided that each one would take a party up the rivers “until we can perfectly satisfy ourselves of the right one.” Clark was to go up the South River and Lewis would ascend the North River.

The next five days were spent traveling up the rivers. On June 6th Lewis said he was convinced the North River was the wrong course because it went too far north. The next morning, to make one final check, he sent two men upriver to a hilltop to visually survey the area. Their report was the river (which had made a bend to the west) made a bend back to the north going that direction as far as they could see. Convinced of his decision Lewis named the North River the Marias River and the party headed back to its mouth.

On June 5th Clark surveyed the countryside from a high ridge and reported “the river runs west of south a long distance, has a strong current, and continued its depth and course; going up further would be useless.” He realized this river would take them into the mountains they were seeking. It is interesting to note here that if Clark would have continued on upriver another dozen or so miles he would have reached the falls the Indians had told them about and assured them of the correct choice.

The Captains show more than a good command of geography and logical thinking required for sound decision making. From the time of the initial examination of the rivers all of the men were certain the North River was the course to follow because “the air and character of this river is so precisely that of the Missouri below.” Lewis says he and Clark were of the opinion the South River was the correct course. Since they were in the minority, they took several days of precious time to decide for certain which river to follow. By doing that extra amount of investigating the Captains did not change the men’s opinion but did get their buy in. Lewis noted, “they said very cheerfully that they were ready to follow us anywhere we thought proper to direct, but they still thought the other was the river (North River).” The Captains could have simply issued the order to follow the South River, but by choosing to get the men’s buy in they exhibited a firm grasp on the principles of sound management.

After the two parties returned from their trips upriver the Captains conferred. By comparing what they found to the information the Indians had given them and the maps they had from earlier Canadian exploration, they became firmly convinced of the proper route. They were satisfied they had collected all the facts they could to base their decision on short of actually finding the falls. In a final show of sound leadership and to show the men that the input they had solicited was important and was considered, the Captains decided that Lewis would take a small party overland up the South River until they reached the falls. Lewis would then send a messenger back downriver to Clark who would be coming upriver by boat with the main party. This final arrangement cemented the men’s buy in.

So we see how the Captains minds worked. This major problem was resolved by working from simple to complex; gathering all possible data; including everyone in the process; using their considerable knowledge of geography; and using logic to reach a final conclusion.

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