Are there any identifiable markings anywhere from the Lewis and Clark
Expedition. i.e.tree markings posted by Capt.Clark or the grave of the
party member who died.Thanks---Ed Harrison

Without doing any research, I do know that there is at least one piece
of physical evidence; I have seen it, and you can see it, too.

At the Pompey's Pillar National Monument in Montana, William Clark's
carved signature has been preserved under glass, where it can be
viewed by the public:

http://www.mt.blm.gov/pillarmon/graphics/clarksig.jpg

Same thing different article I 
believe:

http://www.nationaltrust.org/magazine/archives/arch_story/101001.htm

But this article states:
Pompeys Pillar, 28 miles from Billings, Mont., bears the only physical
evidence of the Lewis & Clark expedition. (BLM)

-AI

This video, from The Discovery Channel, may be of interest:

http://shopping.discovery.com/stores/servlet/ProductDisplay?catalogId=10000&storeId=10000&productId=24251&langId=-1&search=Y&searchKey=-476372419

A quote from the description of "The Search for Lewis and Clark"
video:

"Ken Karsmizki, a historical archaeologist at the Museum of the
Rockies, has spent the last fourteen years on the trail of Lewis and
Clark and he has announced the first discovery ever of a Lewis and
Clark site. Follow Ken as he uses intensive archival research,
geophysical survey, and methodical archaeological excavations to
locate the evidence. Old fashioned detective work and advanced
scientific applications yield definitive proof of one of the most
important journeys in American history."

More about Ken Karsmizki's research:

http://www.eastoregonian.com/stories/99/mar/12/story1.html

http://www.montana.edu/wwwpb/univ/lewis.html

I found the hour-long video interesting, combining the modern day
search with reenactments.  They covered several locations along the
route (as pinkfreud mentioned).  There was very little left behind to
find.  Maybe the most important items were the journals.

I'll mention this other video by Ken Burns.
http://www.pbs.org/lewisandclark/

Good luck in your search!

One interesting artifact that has not yet been found is the
collapsible metal boat that the expedition carefully buried for later
use during their trip.  I believe it was mentioned in the Ambrose
book.
Brad-ga