This is the white form of Rhododendron arboreum, entry 797 in the Flowers of the Himalaya by Polunin and Stainton. We were too late for the red version, locally called “burans”, which blooms in spring. The white ones occur at higher altitudes, and we were told that they appear in June and July. These are early specimens, on the trail up from Dodital to Darwa.