This is an Oregon Trail memorial at Ft. Casper Wyoming. I somewhat wonder if the medallion on this one came from an older monument, as the medallion is a very common site along the trail on older memorials. At some point prior to World War Two a significant effort was made to place such memorials commemorating the trail, which in many locations had become state highways.
This is an even older Oregon Trail Memorial, also located at Ft. Caspar. As can be seen from the monument, it was placed in 1914. During this period, traveling on the trial itself was very common, as nearly every stretch of it was some sort of local road. Indeed, in some parts of Wyoming, this is still the case.
Once again, these monuments probably really do not belong here, but they are strongly associated with the history of Western movement, which involved a lot of sacrifice of all sorts by all involved.