Which river did Lewis and Clark travel most of their journey on? Was it the Ohio?

No. The Ohio flows east of the Mississippi River.

Lewis and Clark's journey took them west of the Mississippi on the Missouri River.

Nope. Different river.

http://www.nationalgeographic.com/lewisandclark/

http://www.pbs.org/lewisandclark/

http://en.wikipedia.org/wiki/Lewis_and_Clark_Expedition

http://www.lewis-clark.org/content/content-channel.asp?ChannelID=54

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No, Lewis and Clark did not travel most of their journey on the Ohio River. The Ohio River was actually the starting point of their expedition. From there, they traveled upstream on the Mississippi River to reach their ultimate destination in the American Northwest.