This canyon is a real gem that sits smack in the middle of a state that doesn't seem all that interesting. We stopped by during the tail end of a Yellowstone/Montana road trip. While it isn't a destination canyon, I'd definitely recommend stopping by if you ever find yourself near Twin Falls, Idaho.
Here are some good directions for getting to the canyon:
PARK HERE: 43 04' 31" 114 18' 21"
The road to the top trailhead SUCKS, so don't bother driving up there and ruining your vehicle. Plus, if you park at the bottom, you get to do the canyon twice (awesome!). This canyon is short, so it will never be worth setting up a shuttle.
Starting at the diversion dam, walk up the west side of the drainage until you see a very easy entrance. Walk down into the the canyon then hike upstream through a stunning slot for about an hour until you get to a 12 foot dryfall. This obstacle will be challenging for small kids and old folks, but easy for everyone else. Consider turning back here if it seems too tough, because there is not a lot of canyon to see above this point. Some folks might enjoy a handline here. Nothing in this canyon is even close to being bolt-worthy, so please leave your bolt kit at home.
After you upclimb the dryfall, hike for about 10 minutes until you reach a wide open wash full of river rocks. Turn around here and enjoy your trip back down Black Magic Canyon.
Here are the coordinates for the turn back point: 43 04' 51" 114 17' 51"
Most small children (3-6) will love this canyon. There are dozens of tiny passageways under the rocks that are just their size. Our son had a blast going through them!
Carrying a small child through this canyon is a LOT of work, and somewhat dangerous due to the unusual overhangs that are difficult to dodge. FAR more work than Little Wild Horse. Leave your babies at home for this one.
There are dozens of opportunities to smack your head in this canyon, so helmets are recommended for this hike.
If there is water flowing through this canyon, then don't go in. There is a dam above that periodically releases water for irrigation. So before you go call the Big Wood Canal Company at 208-886-2331 to check the water release schedule.
Expect a car-to-car time of 2-3 hours.