(Vancouver, WA)  --  Police in Vancouver are warning women who frequent a popular walking trail of a man who's been known to accost and grope female victims.  Authorities say the man has been riding a skateboard along the Burnt Bridge Creek Trail, which runs through the heart of Vancouver.  Police have received two reports this week of a man groping two women along the trail and exposing himself to one of the victims.  The man is described as being in his 20s, having shaggy hair, wearing a white t-shirt and cargo shorts, and either riding or carrying a skateboard.