Last Sunday was a sad day for me. It was Aug. 20, the bicentennial anniversary of the day Lewis and Clark left North Dakota forever. I spent the afternoon out at Fort Lincoln with Tracy Potter and about 50 others who had gathered to observe the denouement of Lewis and Clark's sojourn in North Dakota.

Given the endlessness of the bicentennial (2003-06), with nearly a decade of warm-up activities before that ("Undaunted Courage" by Stephen Ambrose, Ken Burns' splendid documentary, the blossoming of the Fort Mandan Interpretive Center), I did not expect to lament the passing of the historical commemoration of Jefferson's pet exploration project. Almost everyone I have talked with for the past year, including professional historians, has confessed to being "Lewis and Clarked out."

But I was overcome with sadness as I sat in the ceremonial earthlodge at On-A-Slant Village. Lewis and Clark were leaving us. Their boats were traveling 80 to 90 miles a day now, downstream. Their minds were bent on St. Louis. They were not coming back.

The bicentennial has been extremely good for North Dakota.

The four strands of the expedition had re-entered what would become North Dakota between Aug. 2 and 11, 1806, some by way of the Yellowstone and others by way of the Missouri River. All of the strands reunited at Reunion Bay on Aug. 12, 1806, one day after poor Meriwether Lewis was accidentally shot in the buttocks by his otherwise trustworthy waterman, Pierre Cruzatte.

Between Aug. 14 and Aug. 17, the expedition's leadership (now principally Clark; Lewis was nursing his wound and his humiliation) engaged in hectic diplomatic activity with the Mandan and Hidatsa people. As usual, Clark preached peace and commerce, but what he really wanted was a Mandan or Hidatsa delegation to accompany the expedition all the way to Washington, D.C., to meet the curious and artful President Jefferson. In the end, after much persuading and the upping of the proposed compensation package, White Coyote, Sheheke-shote, agreed to make the immense journey, hoping, no doubt, that his participation would bring lasting benefits to his people. Sheheke-shote had been the expedition's principal Indian friend during its five-month residency at Fort Mandan, Nov. 2, 1804-April 7, 1805.

Aug. 17, 1806, was a day of farewells. The expedition said goodbye to the Hidatsa, to the Mandan, to the Charbonneau family and to expedition member John Colter, who had decided to return to the wilderness to try his luck in the beaver pelt trade. Clark paid Toussaint Charbonneau $500, 331/3 cents for his interpreting services, plus payment for the use of a tepee and a horse. A few days later, Clark would express his regret that the U.S. Army had no way of rewarding Sakakawea for her contributions to the success of the expedition. Clark had also fallen in love with Sakakawea's infant son Jean Baptiste (Pomp) and he was already proposing ways in which he could formally adopt Pomp, or at least supervise his education in St. Louis.

On Aug. 17, the Mandan people said goodbye to Sheheke-shote, his wife Yellow Corn, their son and Rene Jusseaume and his Mandan wife and two children. There was much crying and great grief. The Mandan were not sure they would ever see Sheheke-shote again. What Lewis and Clark were proposing was an epic journey to a faraway place, where no Mandan had ever been, and the journey began with a run through hostile Sioux country. The Mandan anxiety was only slightly misplaced. Sheheke-shote would be gone for more than three years. The U.S. Army's first attempt to get him home (1807) would be turned back in northern South Dakota not by the Sioux but by the Arikara, who had sent their trusted emissary off to see the Great Father, and he had died in the nation's capital.

It is impossible not to wonder what was going on in the mind of Sakakawea as she stood on the shore on Aug. 17, 1806, watching the Corps of Discovery prepare for departure. She had spent a year and a half with the expedition. She had crossed half the continent with Lewis and Clark. She had nursed her infant son all the way out to Oregon and all the way back. She had nearly died twice near the Great Falls of the Missouri in the summer of 1805, once in a flash flood and a second time from a bout of infection and fever. William Clark had helped to save her life both times. She had been reunited with her birth people on the Montana-Idaho border. The chief of the tribe, the Lemhi Shoshone, had turned out to be her brother Cameahwait. In the Shoshone village, she had met the Indian man to whom she had been betrothed in early childhood. At the Pacific Ocean, she had seen a whale. On the return journey, she had guided Clark's party over Bozeman Pass. Even Clark said that her presence had been a critically important sign that the expedition had peaceful intentions.

Now, it was over. She was back in the Mandan-Hidatsa world. Clark and the expedition were leaving forever. Charbonneau was staying behind. We would give anything to know Sakakawea's thoughts on Aug. 17, 1806. Of course, she did not keep a journal. The expedition's six journal keepers were too busy that day to pause to describe her demeanor. Was she crying or laughing? Trying to keep her son from crawling into the boats or holding him quietly in her arms? Gravitating toward or away from Charbonneau? Reconnecting with her Hidatsa women friends or standing stoically alone on shore as romantic novelists like to see her? We don't know.

All we have is silence - and of course the marvelous Amy Mossett, who does not impersonate Sakakawea, but who has traveled farther into her soul than anyone who has ever tried.

Once all the hugs were exchanged, and all the tears of parting had been shed, and everyone in the descent party was on board the canoes, the expedition dropped down to the site of Fort Mandan. Clark had one more farewell in mind. He left the flotilla and walked up to the fort site. He discovered that Fort Mandan had burned to the ground. Only a small portion of the fort remained. Clark believed that the fire had been an accident -which means lightning or a prairie fire. There is something melancholy (and valedictory) in this picture of Clark alone at the charred remains of Fort Mandan. It had been a snug home, the site of the expedition's most successful relations with American Indians, and the location of the expedition's most reliable ethnographic study of plains Indian culture. Now, it was a ruin.

On Aug. 18, 1806, the expedition began its rush to St. Louis, eating the Missouri in great gulps. On the upward journey, nine to 15 miles was a good day. Now, 75 miles was an unremarkable progress.

Clark paused long enough on Aug. 18 to ask Sheheke-shote about the abandoned villages at the site of today's Bismarck and Mandan. Sheheke-shote, who grew up at On-A-Slant, told the story of the 1781 smallpox epidemic and subsequent Sioux aggressions, and the story of the Mandan migration to the Hidatsa homeland at the mouth of the Knife River.

He also told the origin story of the Mandan people. And William Clark had the dignity and respect to cast the story in the journals in the phraseology and the cadence of the King James Bible's book of Genesis.

Two days later, the Lewis and Clark Expedition passed out of North Dakota forever.

We will miss them sorely.