Right off 86 just south of American Falls is the Massacre Rocks State Park. There are some nice trails along the freeway with good views of the Snake River and some rocks, which I assume are massacre rocks, so named by emigrants moving along the Oregon Trail who had to watch for attacks by the Shoshone.
I found it interesting that I was on the Oregon and California Trail....in Idaho. At least call that section the Idaho Trail. I guess nobody wanted to stop here, probably because they didn't want to die to the Shoshone.
Nice hike though, great area to stretch your legs or walk your dog if you have been driving for a long time or just want to see the river and some big rocks. There is a visitors center there (which was closed because of the covid-19 stuff), a campsite, and boat ramp. Worth checking out if you are in the area.