Yarrow is native to the western slopes of the Rocky Mountains. It's common name is Achillea millefolium, historically named after Achilles the warrior, due to it's association to being used on the battlefield. It is used for colds, flus and fevers, painful or suppressed menses, bleeding and hemorrhoids. "Having blood-regulating properties, yarrow is specific for urogenital problems, especially those associated with women. It is considered a specific antihemorrhagic wound remedy and when crushed or in powder form can be applied topically or taken internally for any condition of acute bleeding, especially from cuts and abrasions" according to Michael Tierra in The Way of Herbs.
Great to have handy when out in the back country!