California's Central Valley is a large, flat valley that dominates the geographical center of the U.S. state of California.It is 40 to 60 miles (60 to 100 km) wide and stretches approximately 450 miles (720 km) from north-northwest to south-southeast, inland from and parallel to the Pacific Ocean coast.alifornia's Central Valley is a large, flat valley that dominates the geographical center of the U.S. state of California.