Crossing over to Sand Lake River, Mr. Thompson found a small post of the North-West Company, and, descending this stream, came to Sand Lake. By portage, reaching a small stream, a tributary of St. Louis River, he soon arrived at that river itself, with its rapids and dalles, and at length reached the North-West trading post near the mouth of the river, where it joined the Fond du Lac.
Having come to Lake Superior, the party could only obtain a dilapidated northern canoe, but with care it brought them, after making an enormous circuit and accomplishing feats involving great daring and supreme hardship, along the north shore of the lake to Grand Portage. On hearing his report of two years' work, the partners, at the annual meeting at Grand Portage, found they had made no mistake in their appointment, and gave him the highest praise.
The time had now come, after the union of the North-West Company and the X Y Company, for pushing ahead the great work in their hands and examining the vast country across the Rocky Mountains. The United Company in 1805 naturally took up what had been planned several years before, and sent David Thompson up the Saskatchewan to explore the Columbia River and examine the vast "sea of mountains" bordering on the Pacific Ocean. The other partner chosen was Simon Fraser, and his orders were to go up the Peace River, cross the Rockies, and explore the region from its northern side. We shall see how well Fraser did his part, and meanwhile we may follow Thompson in his journey.
In 1806, we find that he crossed the Rockies and built in the following year a trading-house for the North-West Company on the Lower Columbia. Thompson called his trading post Kootenay House, and indeed his persistent use of the term "Kootenay" rather than "Columbia," which he well knew was the name of the river, is somewhat remarkable. Coming over the pass during the summer he returned to Kootenay House and wintered there in 1807-1808. During the summer of 1808, he visited possibly Grand Portage, certainly Fort Vermilion. Fort Vermilion, a short distance above the present Fort Pitt, was well down the north branch of the Saskatchewan River, and on his way to it, Thompson would pass Fort Augustus, a short distance below where Edmonton now stands, as well as Fort George.
He left Fort Vermilion in September, and by October 21st, the Saskatchewan being frozen over, he laid up canoes for the winter, and taking horses, crossed the Rocky Mountains, took to canoes on the Columbia River again, and on November 10th arrived at his fort of Kootenay House, where he wintered. On this journey, Thompson discovered Howse's Pass, which is about 52 deg. N. latitude.
In 1809, Thompson determined on extending his explorations southward on the Columbia River. A short distance south of the international boundary line, he built a post in September of that year. He seems to have spent the winter of this year in trying new routes, some of which he found impracticable, and can hardly be said to have wintered at any particular spot. In his pilgrimage, he went up the Kootenay River, which he called McGillivray's River, in honour of the famous partner, but the name has not been retained. Hastening to his post of Kootenay House, he rested a day, and travelling by means of canoes and horses, in great speed came eastward and reached Fort Augustus, eight days out from Kootenay, June 22nd, 1810. From this point he went eastward, at least as far as Rainy Lake, leaving his "little family" with his sister-in-law, a Cree woman, at Winnipeg River House.
Returning, he started on October 10th, 1810, for Athabasca. He discovered the Athabasca Pass on the "divide," and on July 3rd, 1811, started to descend the Columbia, and did so, the first white man, as far as Lewis River, from which point Lewis and Clark in 1805, having come over the Rocky Mountains, had preceded him to the sea. Near the junction of the Spokane River with the Columbia, he erected a pole and tied to it a half-sheet of paper, claiming the country north of the forks as British territory. This notice was seen by a number of the Astor employés, for Ross states that he observed it in August, with a British flag flying upon it. Thompson's name among the Indians of the coast was "Koo-Koo-Suit."
Ross Cox states that "in the month of July, 1811, Mr. David Thompson, Astronomer to the North-West Company, of which he was also a proprietor, arrived with nine men in a canoe at Astoria from the interior. This gentleman came on a voyage of discovery to the Columbia, preparatory to the North-West Company forming a settlement at the mouth of the river. He remained at Astoria until the latter end of July, when he took his departure for the interior."
Thompson was thus disappointed on finding the American company installed at the mouth of the Columbia before him, but he re-ascended the river and founded two forts on its banks at advantageous points.
Thompson left the western country with his Indian wife and children soon after this, and in Eastern Canada, in 1812-13, prepared a grand map of the country, which adorned for a number of years the banqueting-room of the bourgeois at Fort William and is now in the Government buildings at Toronto.