Dan: A great place for both your target species is Market Lake, which is either a Wildlife Management Area or a National Wildlife Refuge. It's not too far at all from IF, just up I-15 to the Roberts area. I had both those species at that location in early June. We only heard the bittern, however.
Another fantastic area for birding is south of IF, in the Mink Creek Recreation Area, just up the hill from Pocatello (50-65 miles south of IF). Kinney Creek, Cherry Springs, and Justice Park are birding locations within the larger Recreation Area, and they hold lots of good western birds, such as Western Scrub Jay, Long-eared Owl, Virginia's, McGillivray's, and Black-throated Gray Warblers, etc. I got my life Flammulated and Northern Saw-whet Owls in those locations as well.
Feel free to IM me if you'd like more specific information.
Steve in Houston
P.S. If you can get up Wolverine Canyon, near Blackfoot, you can find many of the species mentioned in the Mink Creek area, without the driving distance. Good luck.