Rainbow Basin (Rainbow Lakes)

Boise National Forest, Mountain Home Ranger District (Trinity Mountains, Elmore County)

“Campsite at Heart Lake, Rainbow Basin” by AmblingGent , Creative Commons

Rainbow Basin packs nine glacier-carved lakes into a single short trail in the Trinity Mountains, in a forest that, as the National Forest Foundation puts it, may not have as many alpine lakes as other parts of Idaho. One steep climb gets you over the divide, and after that you can pick a lake, set up camp, and spend the next day wandering between the others.

Getting there takes more effort than the hike. The trailhead is a long drive on dirt roads, and snow can keep it closed until July.

The hike

The trail starts at Big Trinity Lake Campground, and the hardest part comes first. The Idaho Trails Association says the first mile gains 670 feet and is mostly unshaded. A 2016 Magic Valley article puts the climb at 620 feet through recently burned ground. One Boise hiking blog calls this stretch to the saddle by far the most difficult part of the trip. From the divide you get your first look into the basin, including its first lake far below and Trinity Mountain with its fire lookout.

The descent into Rainbow Basin is gentler, with about a dozen switchbacks according to the same blog, and the trail winds through tall trees and over small streams. The Idaho Trails Association lists the nine lakes in order: Green Island, Little Lookout, Fiddle, Big Lookout, Heart, Big Rainbow, Middle Rainbow, Little Rainbow, and finally Hideaway. Only two sit directly on the trail. The rest are reached by spurs a quarter to half a mile long. The Forest Service’s order for the area names the spur trails one by one, from the Green Island Lake Trail to the Middle Rainbow Lake Trail.

Each lake gets its own description in published accounts. The Magic Valley article says green scum at Fiddle Lake’s edge suggests it may not be the best place to let a dog swim. It calls Little Lookout the smallest of the nine and places Big Lookout and Heart on the flanks of Trinity Mountain. Heart Lake, the Boise blog says, is named for the deep heart-shaped basin it fills. Big Rainbow sits beneath a dramatic rock wall, and the blogger judged it the largest lake on the route from a topographic map. The last mile to Hideaway Lake climbs nearly 700 feet, per the Idaho Trails Association, and the Magic Valley article puts Hideaway at 8,420 feet.

Distances vary by source. The Forest Service calls it the 4-mile Rainbow Basin Trail System. The Idaho Trails Association says 4.4 miles one way, 8.8 miles round trip without the spurs, and about 12.8 miles if you visit all nine lakes.

Trinity Mountain, the Forest Service says, is the tallest peak in the range at 9,700 feet, and its summit is the highest drivable point in Idaho. A short, steep hike from the road reaches the lookout. The Idaho Trails Association says Idaho Fish and Game stocks the lakes with rainbow and cutthroat trout, and fishing is a big part of the draw. The Magic Valley article says day hikers carrying fishing poles make up much of the traffic.

The basin sits in a cluster of lakes. The Forest Service describes Big Trinity, Little Trinity, and Big and Little Roaring River Lakes nestled together below the peaks of the Boise Mountains, with campgrounds and rental cabins nearby. The same 2016 article also reported a problem worth knowing about: visitors had been scarring trees around campsites with hatchets and knives, leaving many at risk of dying. Leave the trees alone.

Tips

Plan for July or later. The Forest Service says snow can make the area inaccessible until early July, and the National Forest Foundation says melting snow can block road access through June. A 2016 article says the vehicle gate opens July 15 and closes Nov. 10; confirm current dates with the Mountain Home Ranger District.
Budget time for the drive. One Boise blogger says the trailhead is under 40 miles from Boise in a straight line but about three hours by road. The Forest Service says FS road 172 is dirt and not recommended for trailers. Sources disagree on whether you need four-wheel drive.
Carry a map or GPS. One route guide says the path is not well marked and is mostly exposed, so bring sun protection and plenty of water. Another trip report calls the trail well marked. Plan for the first.
No bikes, motors, or stock. A Forest Service order in effect through March 1, 2030, prohibits bicycles and motor vehicles on the trails, saddle and pack animals, motorboats, and any motor that can propel a watercraft anywhere in the basin.
Expect company on summer weekends. One AllTrails review from August 2026 describes crowds and trash near campsites. Pack out everything.

Camping

The Idaho Trails Association says every lake on the trail has at least one good campsite. At the trailhead, it counts 17 campsites at Big Trinity Lake Campground, plus other sites at the smaller lakes you can drive to. We could not find a Forest Service source on whether a permit is needed for backcountry camping in the basin, or on specific food storage rules. The Forest Service does say moose and black bears are occasionally seen in the area, so store food accordingly, and call the Mountain Home Ranger District before you go.

Inside Intel: Heart Lake is the one to know about, because two separate trip reports say it has only one campsite. One blogger stayed there undisturbed for two days in early fall. A parent on a family trip found the site already taken and had to push on to Big Rainbow Lake. If Heart is your goal, have a backup. A 2016 blog found several campsites around Big Lookout Lake, though most were full. That writer said Heart and Big Rainbow, about a mile farther, would both make good base camps.

Trail facts

Distance: About 8.8 miles round trip without side trips (4.4 miles one way per the Idaho Trails Association; the Forest Service says a 4-mile trail system). About 12.8 miles to visit all nine lakes.
Route type: Out and back, with short spur trails to most lakes
Difficulty: Moderate (the Idaho Trails Association rates it 3 out of 5)
Elevation: About 1,600 feet of total gain over the main trail, per the Idaho Trails Association. Hideaway Lake sits at about 8,420 feet.
Campsites: Dispersed lakeside sites. At least one per lake, according to the Idaho Trails Association. Heart Lake reportedly has only one.
Water: Lakes and small streams along the trail. Treat all water. The first mile to the divide is mostly unshaded.
Permits: None found. Confirm with the Mountain Home Ranger District.
Food storage: No specific rule found. Black bears are occasionally seen in the area.
Dogs: One route guide says leashed dogs are allowed. Not confirmed with the Forest Service.
Restrictions: No bikes, motor vehicles, pack or saddle animals, or motorized watercraft (Forest Service order 0402-01-111).
Trailhead: Big Trinity Lake Campground, Trinity Recreation Area, reached via Featherville and Forest Road 172
Season: July or later, depending on snow
Last verified: September 28, 2026

The Lowdown

Nine lakes, one good night:

Wherever you end up camping in the basin, a good pad makes the lakeside ground a lot kinder. See which pads testers recommend.

See the picks →

Where this comes from

This page draws on the sources below, along with other guides and trip reports. Links go to the original pages.

Before you go: This page is based on published trail guides, trip reports, and reviews, along with official park and agency information where we could find it. It’s meant to help backpackers discover new trails, not to replace current, official information. Conditions, closures, permits, campsites, and water sources change, and some details here may be out of date or wrong. Confirm everything with the managing agency and check current conditions before you head out, and don’t rely on this page alone for safety or navigation. Backcountry travel involves risk.