Complex sentence: The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean.
Split into simpler sentences: The river rises in the Rocky Mountains of British Columbia, Canada. Flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean.