The Rossendale Valley (also called the "Forest of Rossendale") is an area North West England, in Lancashire. The area is in Rossendale. It is made up of the steep valleys of the River Irwell and its tributaries. These flow from the Pennines. They then go south into Greater Manchester. They cut through the open moorland. The area has a lot of these, even though a long time ago they were called "forests".