Great Boulder Depot Explosion of 1907. A stereographic view of the scene after the explosion at the Boulder freight depot at 9th Street and the tracks on 10 Aug. 1907. Two buildings at 945-947 Walnut, one street to the north, are visible in this view; they housed the Boulder Grocery Company (wholesale grocer, at 946 Walnut) and the Boulder Iron Works (at 945-947 Walnut)