Meriwether Lewis and William Clark, younger brother of George Rogers Clark, were sent by President Jefferson to explore the Louisiana Territory. They started up the Missouri River in May of 1804 and reached the Pacific Ocean in November of 1805. They wrote reports on the plants, animals, Indians, soils, rivers, type of country, etc. It was a scientific, as well as an exploring, undertaking. On the return trip, completed in September of 1806, Lewis and Clark separated for part of the journey to take different routes. There were between forty and fifty men in the party. All but one returned safely. They had been instructed to avoid trouble with the Indians and to find a pass over the Rockies; both instructions were carried out. Clark's diary makes good reading and provides an easy and enjoyable way to take the trip over again.

Apparently Jefferson was not bothered by the fact that he ordered the expedition to go across the Rockies beyond our western border. Captain Robert Gray had sailed into the mouth of Columbia River in 1792; in fact, the river got its name from his ship. Then the Lewis and Clark expedition came down the Columbia to the Pacific (1805) and half a dozen years later the permanent settlement at Astoria, established by John Jacob Astor, was a fur trading post near the mouth of the river. These facts combined to give the United States its claim to the Orgeon Territory which we acquired in 1846.