Google has created an online library of maps - a digital atlas. And many are interactive. For example here is a three-layer map of the route of Lewis and Clark in 1804-06. Google allows me to embed it here.
Map from the David Rumsey Map Collection. Use the menu at the upper left to show (1) The hand-drawn map published in 1814 with a slider to control how opaque it is, (2) their route in both direction, and/or (3) their 541 camp sites. Right now I can’t get the route and camp sites to show. See the same map at Google.
See much more at Google Map Gallery.