The Western River Expedition was an attraction planned for the Magic Kingdom. It would have been a lavish tour of the Old West in the manner of Pirates of the Caribbean. However, the company learned that what people really wanted was more buccaneers, so it was scrapped in favor of another PotC ride.
The talented David Witt has made a short series of animations based on the original Marc Davis concept art for the WRE. You can view them at Vimeo here: Western River Expedition: Last Roundup on Vimeo