The Forest Service maintains several campgrounds in the upper Bitterroot (www.fs.fed.us/r1/bitterroot [1], late May–late Sept.), mostly off the beaten path. A couple are handy for casual campers who don’t want to get too far off the highway.
Indian Trees ($10) is six miles south of Sula, right next to Lost Trail Hot Springs [2] at a location where Flathead women once spiked ponderosa pines to extract sap, which was used as a sweetener.
Lewis and Clark camped at Spring Gulch ($12), and so can you. The campground is right on the East Fork River, five miles north of Sula on Highway 93. Right behind the Sula Store (7060 Hwy. 93 S., 406/821-3364, $13 tents, $18–20 RVs, $40–90 cabins) are campsites and cabins (complete with bedding, but the cheapest require a short walk to the bathhouse) at the beginning of the canyon leading from Ross’s Hole.
There are several Forest Service campgrounds up the West Fork Road; Sam Billings is a lovely free spot (no water) near the Boulder Creek trailhead, and there’s another campground past Painted Rocks Lake at Alta ($8).
Links:
[1] http://www.fs.fed.us/r1/bitterroot
[2] http://www.moon.com/destinations/montana/missoula-and-northwestern-montana/the-bitterroot-valley/the-upper-bitterroot/recrea/hot-springs