Our best guess for this caterpillar “floof” is the blue-gray dagger moth caterpillar. According to BugGuide, a resource we consult, this is a large and very difficult genus (73 described species and several to be described). This species is found in dry forests of western North America and uncommon to rare for unknown reasons. The caterpillars are actually green, but the extremely long and dense white hairs conceal their bodies. And although they look pettable it’s probably better to err on the side of caution; the hairs may be barbed and irritate your skin. Caterpillars are specialists, feeding on Ceanothus species in the buckthorn family, particularly snowbrush (C. velutinus). The medium, powdery blue-gray moths are most numerous in late June and July. 
Photo by Noel Moon on 7/21/20 in Missoula, MT.