Color cover of a souvenir postcard booklet from 1929 showing a ship entering into the Soo Locks in Sault Sainte Marie, Michigan. The Soo Locks, located on St. Marys River between the United States and Canada, provide ships safe passage around the rapids in the canal. The first locks in this canal were built in 1855, and have been improved upon ever since. The locks are the busiest, based on tonnage passing through, in the world. This postcard is part of the "Souvenir of Sault Ste. Marie, Canada" souvenir postcard booklet.