Rex Ziak will speak about Dismal Nitch at the next In Their Footsteps lecture on Nov. 20.

ASTORIA —Lewis and Clark’s arrival at Fort Clatsop contains one of the last remaining mysteries of their entire expedition.

The events are so confusing that Lewis and Clark authors, from Bernard DeVoto to Stephen Ambrose, skipped over this history in their writings.

What we know for sure is this: On Nov. 27, 1805 the Corps of Discovery paddled around the tip of Tongue Point and become stranded there. Ten days later, on Dec. 7, they arrived at the site of Fort Clatsop.

These mysterious days will be the topic of the next In Their Footsteps free speaker series event at Lewis and Clark National Historical Park’s Fort Clatsop. At 1 p.m. Sunday, Nov. 20, local author and researcher Rex Ziak will present “‘No account of Capt. Lewis … I fear Some accident has taken place’: The Untold (and Unknown) Dramatic Story of Lewis and Clark’s Search for a Winter Campsite Near the Pacific.”

What happened during those 10 days? Why such a long delay at Tongue Point? What was William Clark doing all that time, and where did Capt. Lewis go?

Did Clark think that Lewis had been ambushed by Indians or drowned? And is it true that Lewis had given up on camping near the ocean and was preparing to build a winter camp somewhere near the Cascades?

Is it also true that the existence of Fort Clatsop can be attributed not to Lewis or Clark, but instead to the extraordinary efforts of just one individual?

These questions and many more will be explored as this program retraces, day by day, this little-known local Lewis and Clark history.

Ziak, who spent a decade in study, revealed these details in 2002 when his book “In Full View” was published. His writing is used today as a source of information by other scholars, including Gary Moulton, who relied on it during a recent project.

Three of Ziak’s books including “In Full View” are available from the Lewis & Clark National Park Association bookstore in the Fort Clatsop visitor center. There will be a book signing at the bookstore following his presentation.

This monthly Sunday forum is sponsored by the Lewis & Clark National Park Association and the park. The program will be held in the Netul River Room of Fort Clatsop’s visitor center and is free of charge.

For more information, call the park at 503-861-2471 or check out www.nps.gov/lewi or Lewis and Clark National Historical Park on Facebook.