Rainbow Lake (Boulder)

Drainage: Boulder
Approaches: Approximately 22.5 miles round trip from the Box Canyon trailhead on Trail #27 then #28, with roughly 3,200 feet of climbing. All on trail. The Upsidedown Trail is 12 miles one way with 4,000 up and 1,000 down.
Elevation: 9,448 feet
Fish: Rainbow trout, common and self-sustaining. Yellowstone cutthroat, common and stocked with some natural reproduction. Montana FWP.
Coordinates: 45.27254, -110.12745
Bugs: Mosquitoes, just bad enough to be annoying.

Getting there

From the Box Canyon trailhead take Trail #27, then #28, then #211. The Upsidedown Trail gets you here too. It is on trail either way.

We came at it across the plateau from a camp at Wounded Man, working down from Pipit on the way to Mirror. We hit the chain from the top and dropped through it over about an hour, from 9,765 feet down to 9,448.

The hike

This is one page for six lakes. Fish and Game numbers them two through seven and does not give them separate names, so they are treated here as one water.

They run from 9,407 feet at the bottom to 9,765 at the top, and they are not all alike. The bottom lake is the big one at 26 acres and 30 feet deep. Number three is 8 acres, number four is 10.5 and the deepest of the chain at 35 feet, and the three upper lakes are smaller again, from 2.2 acres to 9.6.

We walked the four upper ones. Numbers three and four sit below the others and we did not reach them.

The fishery is being actively rebuilt. Rainbows have been self-sustaining here since a 1949 plant. Cutthroat were first put in back in 1932, and FWP has been stocking them hard for the last three years — 13,000 into the bottom lake in 2023, again in 2024, and again in 2025, with smaller plants into three and four on the same schedule.

Their 2025 sampling shows it working. The bottom lake gave up 11 rainbows averaging 10.6 inches with one at 15, and 28 cutthroat averaging 9.4. Number four turned up rainbow-cutthroat crosses as well, which means the two are already interbreeding.

FWP says there are good places to camp but the firewood is picked over.

Tips & safety

• Navigation: On trail from Box Canyon on #27, #28 and #211, or in on the Upsidedown Trail. Coming across the plateau you drop into the chain from the top.

• Camping: Good places to camp, firewood picked over.

• Fishing: Self-sustaining rainbows and heavily stocked cutthroat, mostly 9 to 11 inches with the occasional fish to 15. The two are crossing.

• Bugs: Mosquitoes, annoying rather than bad.