Twin Sisters West Shaft: December 20, 2018February 1, 2018 This content is for NRMG members only.Log In Register Related posts: Searching for Caves in the Northern Rocky Mountains Mystery Cave aka Mystic Cave West Boulder: Dirty Secrets Lost Creek Siphon: The Carl Froslie Experience My Trip to the Silvertip Mountain Cave System: 2019 West Boulder Cave: West Boulder Cave: The Mystery Continues