Celestial Observations at the
Mouth of "Maria's River"
2-10 June 1805
Contrary to what the natives of the northern Great Plains might tell visitors, winter in these parts is not just a continuum of numbing cold, howling blizzards and drifting snow. Once or twice a month there comes a mild day. It begins like this: the sun, having peeped over the southeastern horizon about 8 a.m., climbs a gently sloping arc westward, reaching an altitude of about 20 degrees above the southern horizon by noon, all the while sweeping the blue-black shadows of leafless trees over wind-burnished snow. Meanwhile the temperature, which at sunrise may have been a brisk -10°F, slowly warms, and by early afternoon nears the freezing point – then, by early sunset, plummets back toward the season's diurnal, sub-glacial level. Rigorous? Yes, but not nearly as rigorous as those winters during the early 1800s when a climatic period known as the Little Ice Age prevailed.
When the worst weather elements enveloped Fort Mandan in their frosty embrace during the winter of 1804-05, little could be done outdoors without risking frostbite or, if far from distinct landmarks, risking getting lost during a blizzard. On the other hand when those rare mild days prevailed, Lewis and Clark either visited their Mandan and Hidatsa neighbors or invited them into Fort Mandan. During these meetings the captains gathered information about the topography, the climate and the people along their intended route. This informationwhich would help minimize the unexpected (at least as far as geography was concerned) – came from those who had traveled where Lewis and Clark hoped to go or had gathered said information from others who had been there. It would be the captains' task to evaluate this second- and third-hand information for themselves as they traveled and correct it where necessary. Clark put much of the geographic information they obtained on a map – now known as "Clark's 1805 Map"1 – that was sent back to St. Louis on the keelboat in April 1805 and from there was forwarded to President Jefferson. The captains kept a copy of the map for themselves.
The Lewis and Clark Expedition left Fort Mandan on 7 April 1805 and continued up the Missouri River. Their route for the first few days was northerly, then the river took and held a northwest course upstream until the Expedition reached a tributary the captains identified as White Earth River. Here, conforming to the information the captains had received at Fort Mandan, the river bent to the south of west.
Although the captain's informants had named such streams as Little Missouri, White Earth, Yellowstone, Milk – the "River which Scolds at all other Rivers"2 – Musselshell, Medicine and the Three Forks and had spoken of other geographic features such as the falls of the Missouri and of three different mountain gates above the falls, the captains had to interpret the location of these features based on their informants' concept of the number of days traveled (or the number of sleeps) between the features. In general, however, the captains were able to reconcile the information they had gathered during the winter and early spring with what they found as they traveled.
The detail from Atlas Map 32a, shown above, indicates that the captains were aware that their informants, after crossing the Yellowstone River a few miles above its mouth, did not follow the windings of the Missouri but took a route through the plains to the south of it. It should not have been surprising to them, then, that they had been provided with few details along the Missouri, itself. Nevertheless, they were completely unprepared for what they found a few days after having passed upstream of the Stonewalls&nspace;White Cliffs area.
On June 2, the Expedition reached a fork in the river that their informants had not mentioned. This was not just another junction of the Missouri with a minor tributary. It was the junction of two major streams. They were of different sizes, to be sure, but each bore important characteristics of the Missouri. The south fork obviously was wider, but the north fork had the Missouri's roiling color. Which river was the Missouri?
The Expedition arrived at the junction too late in the day to explore the rivers. The capains selected a campsite3 opposite the point between the two rivers, and the men pulled canoes and perogues ashore and secured them, unloading only essential equipment. Then, after the travelers had eaten their evening meal and the sky darkened, the captains got ready to make celestial observations for longitude. This junction was just such a one as their commander-in-chief had instructed them to record – a "remarkeable point."
It was a clear night. The moon, just two days short of its first quarter, was 23° above the horizon bearing S78° W when the captains began their observations about 9:30 p.m. A rather dull Mars (magnitude +1.1) hung 4° above and 2Ω° west of the moon. Regulus, the brightest star in the constellation Leo was less than a degree directly below Mars and too close to the moon for a reliable observation. The logical choice of a star to use in a Lunar Distance observation for longitude, therefore (and indicated as such in the Nautical Almanac), was Spica – the brightest star in the constellation Virgo. Spica, that same night, had the near companionship of the planet Saturn, 6° above and 13° to the west of her. A brilliant Jupiter blazed in the sky to the southeast at about 20° above the horizon. It was a magnificent night for star watching, but the captains' attentions were absorbed in making celestial observations, and it required a considerable coordination of efforts to make everything work out right.
An observation of the Lunar Distance from a star was much harder to make than an observation of the Lunar Distance from the sun. The extra difficulty in a Lunar-Stellar observation came not only from the respective angles of the two bodies, but from the need to use torch light to read the angles recorded by the sextant and to read the time shown by the chronometer. Fatigue, after a strenuous day's travel, also took its toll.
Despite the hour and despite the fatigue, the captains made two sets of observations of the Lunar Distance from Spica, for longitude. Each set consisted of eight discrete measurements of the angular distance between the two bodies, plus the time of each measurement. Having finished their observations about 10:30 p.m., the captains retired for the night.
Early the next morning, June 3, the Corps of Discovery crossed to the point between the two rivers and made camp4. Here the Corps would stay until the captains resolved the question as to which river was the Missouri. Shortly after reaching this camp on the point, the captains began taking more celestial observations. They took additional observations on June 9 and 10 after they had returned from their separate explorations up each river. Even before they took these latter observations, they were reasonably certain that the south fork was the Missouri and Lewis had named the muddy north fork "Maria's River" – in honor of his cousin, Miss Maria W[oo]d."5
1. It is Map 32a in the Atlas, Volume 1 of The Journals of the Lewis and Clark Expedition, edited by Gary E. Moulton (13 vols., Lincoln: University of Nebraska Press, 1983-2001).
2. This title, of course, represents what Lewis and Clark understood their Hidatsa informant to have said, as it was repeated to them by their interpreters, perhaps from Siouan to French to English. Inasmuch as the 700-mile-long river the captains named "Milk" flows through a horizon of white clay for many miles, and contributes its burden of whitish silt to the Missouri with a bold, striking effect, especially during springtime runoff, it may be that the word scold is merely the arbitrary expression of an Indian word that the interpreters could not quite translate otherwise.
3. The Expedition's camp for the evening of June 2 (Point of Observation 26) was at or near 47°55'36"N, 110°28'50"W. These coordinates were determined by adjusting and comparing the Expedition"s river survey to the earliest detailed maps of the area, modern maps and by use of aerial photos.
4. The Expedition's camp from June 3 to the morning of June 12 (Point of Observation 27) was at or near 47°55'45"N, 110°29'04"W; altitude 2570 feet above sea level. Lewis and Clark's Map of 1806, Atlas Map 123 (Moulton, volume 1), shows the mouth of Marias River at 111° west longitude whereas Atlas Map 125 (1810) and Atlas Map 126 (1814) both show the mouth at 110° west longitude.
5. "It is true," Lewis admitted, "that the hue of the waters of this turbulent and troubled stream but illy comport with the pure celestial virtues and amiable qualifications of that lovely fair one." But, he rhapsodized as his pulse quickened,on the other hand it is a noble river; one destined to become in my opinion an object of contention between the two great powers of America and Great Britin with respect to the adjustment of the North westwardly boundary of the former; and that it will become one of the most interesting brances of the Missouri in a commercial point of view, I have but little doubt, as it abounds with anamals of the fur kind, and most probably furnishes a safe and direct communication to that productive country of valueable furs exclusively enjoyed at present by the subjects of his Britanic Majesty; in adition to which it passes through a rich fertile and one of the most beautifully picteresque countries that I ever beheld, through the wide expance of which, innumerable herds of living anamals are seen, it's borders garnished with one continued garden of roses, while it's lofty and open forests, are the habitation of miriads of the feathered tribes who salute the ear of the passing traveler with their wild and simple, yet s[w]eet and cheerful melody.
What a thoughtful, impassioned tribute. What was really on Lewis's mind? Geo-politics? Commerce? Geography? The immediate problem at hand? Or the comparative beauty and nobility of "that lovely fair one." In any case, this was truly a "remarkeable point," this little spot on the vast geography of "a country at least two thousand miles in width, on which the foot of civillized man had never trodden."
Funded in part by a grant from the National Park Service, Challenge-Cost Share Program.