Tell Me About The Petaluma River spawned its own type of vessel, the hay scow. These small freighters were about 60 feet in length with two square-rigged masts and a steam driven propeller. One of the most famous, the Alma, is now on display as a museum piece at the Hyde Street Pier in San Francisco. She makes the voyage back home to Petaluma each year for the Petaluma River Festival.