The clear waters and picturesque peaks of Idaho’s mountain lakes are always a treat to take in. What’s even better is a trail that takes you to several of them, offering hikers the opportunity to tailor the route.
Just about 100 miles outside of Boise, you’ll find a Forest Service path that’s perfect for fishing, backpacking, wildlife watching and sightseeing. Rainbow Basin Trail, also called Rainbow Lakes Trail, is a 4-mile out-and-back trek in the Boise National Forest that meanders past nine mountain lakes, creating a choose-your-own adventure of unbelievably blue waters.
The drive up is not for the faint of heart (or stomach). If you’re prone to motion sickness, grab some anti-nausea medication before heading out on the 3-hour drive from Boise. Four-wheel drive is a must for the last 13 miles to the trailhead, which include hairpin turns and steep switchbacks peppered with loose gravel and large rocks.
Despite being tucked up in the mountains northeast of Mountain Home, this is a fairly popular trail. On a Saturday, the main parking lot at the trailhead as well as an adjacent day parking area filled up. We saw about 25 to 30 other people during our four-hour hike. The trail is pedestrian-only, so leave the mountain bikes and motorized vehicles at home.
If you’re not keen on squeezing your hike in between 6 hours of driving, there’s plenty of camping in the area. Big Trinity Lake Campground is a first-come, first-served site with 17 designated camping spots (all were full early Friday when we visited, mostly with folks who were riding dirt bikes or ATVs on the surrounding Forest Service roads). There’s also Little Roaring River Lake Campground and some dispersed spots near Little Trinity Lake picnic area and Upper Roaring River trailhead and along the Rainbow Basin trail itself if you backpack in.
On the trail
Rainbow Lakes Trail starts with a bang — gaining about 500 feet of elevation over the first half mile, much of it with fallen trees, loose rocks and other debris in the way. The Trinity Ridge Fire burned nearly 140,000 acres of the area in 2012, leaving skeletons of burned trees that offer little shade at the beginning of the hike.
Around the half-mile mark, you’ll crest a ridge. This is a great spot to catch your breath and take in the view of the forest below. From here, you can see Green Island Lake to the east and, to the south, the jagged peaks of Trinity Mountain and the fire lookout perched atop it. (If you’re looking for another adventure, you can drive or hike to the summit of the 9,700-foot mountain — the highest drivable point in the state, according to the Forest Service.)
The next mile or so of the trail is a respite from the uphill. Hikers quickly descend into the trees, which offer shelter from the sun. This is a great area to keep an eye out for wildlife — bright yellow tanagers, deer and elk frequent the area, and black bears and mountain lions are sometimes spotted, too, Forest Service officials say. Upon our arrival at Big Trinity Lake, we saw a cow moose taking a dip in the shallows and grazing on aquatic plants.
As you descend from the ridge, the trail begins to wind past the multiple lakes dotting the forest. According to the Forest Service, Rainbow Basin is a cirque that was formed by a glacier — meaning the alpine lakes are relatively small and shallow.
The first several miles of the trail are relatively well-marked with Forest Service signs, each designating the mileage to the next lake. For the most part, the signs are placed at the spur to each individual lake, about a quarter-mile from each.
First you’ll pass Green Island lake before coming to the routes toward Fiddle, Heart and Big Lookout lakes. Next is the trio of Rainbow Lakes — aptly named Big, Middle and Little Rainbow lakes for the rainbow trout you can catch in them. The Rainbow lakes make great destinations to stop for lunch, fishing or photos of the turquoise water in the shadow of the sheer Trinity peaks.
At times, this is a difficult trail simply because of the amount of debris on the path. Around 3 miles into the trail, an entire downed tree laid waist-height across the path. Thanks to rocky crags on one side of the trail and marshes to the other, the easiest route for us was over the tree. You’ll also encounter more loose gravel, as well as trees to duck under, overgrown brush to bushwhack through and multiple creek crossings on log bridges, some of which are partially submerged or coming unfastened from the bank. (Be prepared with a map or GPS app to ensure you don’t wander off the trail when navigating around obstacles.)
The trail winds directly past Little Rainbow Lake before again angling up steeply through a heavily burned area. Here, dozens of bright red and salmon-colored Indian paintbrush cover the sandy hillside. But those and other flora make the trail difficult to follow at times. We turned back here, but met several other hikers headed up the steep grade to the final destination on the trail — Hideaway Lake.
Though the series of mountain lakes are gorgeous, they’re also a hotbed for mosquitos and horseflies in the summer. Our bug spray was no match for the swarms.
Still, the basin of unbelievably blue waters is enchanting. It’s tough to leave the singing birds and pine scent of the forest (and not just because you’ll have to head uphill on what was a refreshing descent on your way in).
There are two routes, both of which require you to head east from Boise on Interstate 84 toward Mountain Home. You’ll stay on the interstate for 40 miles.
At Exit 95 for Mountain Home, take a left onto U.S. 20 east toward Anderson Dam and Pine/Featherville. Stay on this road for 20 miles.
At the intersection for Anderson Dam Road, you can either continue toward Pine and Featherville or turn left onto Anderson Dam Road. We took the latter route, following Anderson Dam Road for 5 miles across the dam spillway.
Next, turn left on Forest Service Road 134. In one-third of a mile, stay right on Anderson Dam Road for 8.7 more miles. Follow signs for Trinity Mountain Road for 6.3 miles, and turn right onto Trinity Mountain Road (Forest Service road 129) where it intersects with House Mountain Road.
From here, the route becomes especially bumpy. Follow the road for 13 miles, driving past the right-hand turnoff to the road 129A spur, which takes you to the fire lookout. Instead, take a right onto Forest Service road 129E (toward Big Trinity Lake Campground) at the intersection for Little Trinity Lake picnic area.
You’ll arrive near the Big Trinity Lake Campground information sign. Head left; turning right will take you around the second half of the campground, which does not offer access to the trailhead. The trailhead is about half a mile from the fork. A vault toilet and potable water pump are nearby.