Rose meadowsweet looks almost too 'garden-like' (in a western civilization sort of way) to be a native plant. But it is indeed native to Western Montana, although you might not see it unless you gain a little bit of elevation. There is a lovely thicket of them just shy of the Lolo Pass summit...
 
This little shrub has oval, toothy deciduous leaves and dense clusters of rose-pink flowers in the summer. You can expect it to get about 3 feet high and as wide. It tends to grow in sunny borders but can tolerate light shade. It likes moist soil but needs good drainage, which is probably why you often find it growing in boulder-fields and rocky chutes. 
 
As with other higher elevation plants, if you plant this shrub down in the valley, where summer temperatures are higher than its preferred range, plan to give it additional water and protection from death ray late afternoon sun. East facing walls and fences are a great choice. 
 
Photo credits:
1st, by Matt Lavin from Bozeman, Montana, USA - Spirea splendens uploaded by Tim1357, CC BY-SA 2.0
 
2nd by Walter Siegmund (talk) - Own work, CC BY 2.5