Idaho Falls, population 60K, is located in the southeastern part of the state, about 75 miles due west of Grand Teton NP. 57% of the people are Mormon so it comes as no big surprise that there's a magnificent Mormon Temple here, shown in the picture below, apparently sprouting out of my hat. Indeed, their temples are magnificent, built to some of the most demanding specs ever. I toured one in Portland, briefly open to the public just after construction was completed. Impressive!
The falls are man-made, providing a 19' drop to power low-head hydro turbines. Low-head hydro dams have several advantages over massive concrete dams. They're easier, quicker and cheaper to build; silt buildup isn't a major problem; and they don't require mountainous or deep canyon locations. They can be built just about anywhere there's adequate water volume.
This is the Snake River, and the City has done a great job of making it an attractive centerpiece. There are paved walking/cycling trails on both sides, lots of grass, trees, topiary and sculptures.