Jefferson found himself in a strange position. The Constitution nowhere delegated to the United States power to acquire territory. But after thinking it over Jefferson felt sure that the people would approve of the purchase. The treaty was ratified. The money was paid. This purchase turned out to be a most fortunate thing. It gave to the United States the whole western valley of the Mississippi. It also gave to Americans the opportunity to explore and settle Oregon, which lay beyond the limits of Louisiana.

Jefferson soon sent out several expeditions to explore the unknown portions of the continent. The most important of these was the expedition led by two army officers, Meriwether Lewis and William Clark, brother of General George Rogers Clark. Leaving St. Louis they slowly ascended the muddy Missouri. They passed the site of the present city of Omaha. They passed the Council Bluffs. The current of the river now became so rapid that the explorers left their boats and traveled along the river's bank. They gained the sources of the Missouri, and came to a westward-flowing river. On, on they followed it until they came to the river's mouth. A fog hung low over the water. Suddenly it lifted. There before the explorers' eyes the river "in waves like small mountains rolled out in the ocean." They had traced the Columbia River from its upper course to the Pacific. Captain Gray in the Boston ship Columbia had already entered the mouth of the river. But Lewis and Clark were the first white men to reach it overland.