There is a geneology of the Clark family that extends at least into the mid 20th century. Any of a number of Lewis & Clark centers from Illinois to Washington could probably help you track it down.
I spoke recently as Gov. Clark at the Bellefontaine Cemetery in St. Louis, where I was reburied in the 1850s. I think I saw one mounted on their office wall.
I know one WC descendent in St. Louis and have met another.
I've portrayed Clark professionally to conference audiences across the nation for almost 17 years. This will tell you more:
You have an admirable ancestor!