Below the Cascades of the Columbia River the Corps of Discovery passed into yet another natural region, the thick rain forest of the Northwest Coast. Many Indian villages dotted the banks of the Columbia, some of them inhabited by people frightened by the coming of strangers. Fortunately the sight of Sacagawea and her baby convinced them that the newcomers were not a war party. Near the mouth of the Willamette River they reentered the world of previously known geography, for boats of George Vancouver's British expedition had penetrated this far up the Columbia in 1792.

For November 7, 1805, Clark was able to note "Ocian in view! O! the joy." In fact, he was premature, for what they were seeing was only the wide estuary of the Columbia. Within a few days, however, Lewis and a few men pushing ahead did reach the coast. Their satisfaction at attaining their long-sought goal was considerably dampened by the weather, the characteristic rain and storms of the Northwest Coast winter. The party was trapped for days on the northern shore of the estuary, unable to move because of high winds and gigantic waves. "All wet and disagreeable" is an expression occurring frequently in Clark's journals, and on November 22, still immobilized, he burst out. "O! how horriable is the day." Their discomfort was not altered by seeing the Chinook Indians paddle their canoes across rough waters the explorers did not dare attempt.

They had arrived where they had longed to be, and they knew that the mountain winter would make the return east impossible for some months. Their immediate problem was to find a place near the coast to wait out the winter. There seemed to be no really suitable spot on the north side of the Columbia. Considering whether to winter on the coast, intolerably wet but offering the possibility of contact with a ship, or to seek some drier inland spot up the Columbia, the captains took the step, rare in the annals of exploration, of taking a vote of the party. Even York, the slave, and Sacagawea, the Indian woman, had their opinions recorded. The final decision was to cross to the south side of the Columbia to seek a location with adequate game and proper timber to build a stockade. After a few days of searching, on December 7 they picked a site on the banks of what is now called Lewis and Clark River some miles from the coast. While Clark set out on the next day for the coast to find a site for a saltmaking camp, Lewis and the men began felling trees for what they would call Fort Clatsop after the local Indian tribe. Here would be their home for the next three and one half months, until March 23, 1806.

It was a sojourn marked not by the fierce cold and snow of the previous winter at Fort Mandan but by rain, storms, and gray skies. They did not starve, but food was neither plentiful nor good. The inability to preserve meat in the damp climate meant that they lived much of the time on spoiled elk, fish, and roots. Relations with the local Indians were not as satisfactory as they had been at Fort Mandan. The captains found many of the natives' customs and attitudes repugnant and thought they demanded too high a price for the food and other goods they furnished. Although the Indians never manifested real hostility, the commanders took strict security measures to insure the safety of the party.

The quest for food kept hunting parties out constantly, elk being the chief game animal. Reports of a whale stranded some distance down the coast led Clark to set out on January 6 to seek this possible source of meat, with a party of eleven men. Sacagawea insisted on going to see the ocean and the big fish, taking her baby and her husband with her. Clark found that the Tillamook Indians had already stripped the whale, but he was able to purchase a few hundred pounds of meat and a few gallons of oil and returned to the fort on January 10.

The captains had had hopes of meeting American or British seagoing traders, from whom they might obtain supplies and send dispatches home, but none were in the area during the winter although there was abundant evidence of their contact with the local people. A Russian ship seeking a location for a new settlement arrived off the mouth of the Columbia just before the Americans left, but they were unable to enter the river and the two parties never met.

The captains did not lack occupation. Lewis resumed his journal-keeping on the first day of 1806, after a lapse of over three months. For the remainder of his stay at Fort Clatsop he devoted himself to making a detailed record of the natural history and human culture of the coast and the region west of the Rockies. Clark has occasionally received credit for the first descriptions of many new species, but it now appears that he simply borrowed material originally written by Lewis, while copying Lewis's journals. At no other time did they devote so much space to the description of plants and animals and the life and material culture of the native peoples, the record of a land little known to the outside world. Included with these descriptions were an unprecedented number of sketches, in the journals themselves, of plants, animals, and artifacts. The number of drawings other than maps in these Fort Clatsop journals far surpasses those found in the rest of the captains' writings, the product of enforced leisure in a strange, new environment. Besides the many plant and animal species pictured, there was a record of the great variety of canoe types, of native clothing, implements and weapons, and diagrams of the local methods of deforming the heads of infants, with the results.

The captains first noted the transition in the Columbia gorge from the dry ponderosa pine–white oak forest on the east to the moist Douglas fir–western hemlock–Sitka spruce forests on the west. Among plant species first described by Lewis are the Oregon crabapple, Oregon grape, dull Oregon grape, and salal (all sketched in the journals and appearing in this volume), along with trees like Sitka spruce, grand fir, and western white pine. Among new animal discoveries were the greater white-fronted goose, the northern fulmar, the eulachon, and the sage grouse (all pictured in volume 6), and also the Columbia black-tailed deer, the steelhead trout, the mountain beaver (which is not a beaver), and the Oregon bobcat. While Lewis wrote, Clark worked on his maps of the first transcontinental journey by Anglo-Americans.

We know much less about the enlisted men, except that they were kept busy hunting and making moccasins for the return trip, and that the captains were sufficiently concerned about veneral disease that they finally asked for a pledge that none of the party would have anything more to do with the native women. Minor illnesses flourished because of the dampness and cold.

Boredom, sickness, a monotonous diet, and the dreary weather all enhanced their impatience to start on the trip for home as soon as they reasoned that the melting snows of the Rockies would allow their passage. The captains knew that the Nez Perces, with whom they had left their horses on the trip west, would head east of the Rockies to hunt buffalo as soon as the snow in the higher mountains receded. They were anxious to secure their horses, cross the mountains, and explore new trails the Shoshones had told them about—a more direct route from the eastern end of the Indian road across the mountains to the Great Falls of the Missouri and also to carry out a separate exploration of the Yellowstone River.

They had planned to leave on April 1, after preparing what food and clothing they could obtain and leaving messages in the fort and with the Indians for any sea traders who arrived after their depature. If any disaster overwhelmed the Corps on the journey home, some record of their achievement might thus still reach the United States. Eagerness to be on the move prompted them to move up the date to March 20, then bad weather and the need to secure additional canoes held them another two days. Lewis and Clark feared that the price the Indians wanted for another canoe would so badly deplete their small stock of trade goods as to cripple their ability to obtain needed supplies on the way home. The captains succumbed to temptation and violated their longstanding and consistently observed rule against stealing Indian property and sent out a party to take an unattended canoe nearby, rationalizing that the Clatsops had taken elk that the expedition hunters had shot and left.

On March 22, Lewis wrote, "we determined to set out tomorrow at all events."