Acronicta impressa

The caterpillar looks just like an arctiid woolly bear, and one may even not suspect that it is not an arctiid until the cocoon is constructed. Arctiid woolly bear cocoons are loose and fragile; those of dagger caterpillars are tough and cannot be torn apart by hand. I have found this caterpillar on wild rose, snowberry, alder and Ocean Spray.