What is this prolific plant?

[bobm]

I have a friend who had a the misfortune of planting snow on the mountain to fill in a small space around tree. Within about 5 years it was a real problem . He still to this day tells me he had to move to get rid of it.

Two years ago I bought snow on the mountain at the Master Gardener's plant sale. I planted it on top of a hill that I had built up surrounded by boulders. Less than a year later ... it be GONE ( killed, maiomed and destroyed ) to their resting place !!! Now I know better.