I found out all about that talcum powder when I went down Lowell Hill road this last July. Also Henness Pass, miles of it and pooled pretty deep in a few places.
The roads in that area must get a lot more vehicular use than down here in the EDNF, because here it's mostly hardpack all the way through the season.
I was astounded by the size of the gravel bars along the sides of the creek past Red Dog. I'm assuming thats all eroding runoff from old hydraulic workings. Almost 150 years later and it's still there, amazing how destructive hydraulic mining was.