I went to the Forest Service's Sawtooth Nation Recreation Area information center this morning to get the full scoop on dispersed camping in the area. The simple answer was essentially, "Anywhere that isn't private property."
"So I can just pull off on any road in National Forest land?"
"As long as you're not blocking the way."
(Looking at a detailed map) "Wow, cool."
"We try to make it easy for people to get out and enjoy this beautiful area."
That means I have a lot of exploring to do.
Meanwhile, this is where I'm camped today. It's not far from Ketchum, a few steps from Trail Creek. And I have a few bars of 4G cell service.