MISSOULA, Mont. (AP) - Historians and scientists have found physical evidence that pinpoints the campsite that Meriwether Lewis dubbed Travelers' Rest in 1805.

The five-year study may persuade the National Park Service to correct the location it listed years ago - off by a mile and a half - in the national register of historic places.

The site joins a very small list of locations along the 8,000-mile length of the Lewis and Clark Trail where physical evidence of the expedition has been found.

Travelers' Rest is now designated a state park.

Indians had camped there for untold years. An Indian guide called Toby brought Lewis and Clark to the site in September 1805 to prepare for crossing the Bitterroot Mountains.

Aerial infrared photography showed evidence of tepee rings. Historical research matched coordinates of latitude and longitude recorded by Lewis and Clark. Archaeological digs turned up a latrine, a late-18th century button and lead.

Vapor analysis verified the presence of mercury beneath the old latrine. Mercury, which does not decompose, was the major ingredient in a powerful laxative carried on the expedition.