 Ledson Marsh has a southern outlet to the north fork of Yulupa Creek.The Yulupa Creek watershed was below the Pacific Ocean floor as recently as the Miocene era, around which time massive uplift and volcanic action formed the massif which comprises the headwaters higher elevations of the watershed of today.Elevations within the drainage basin of Yulupa Creek range from about 430 to 1800 feet (130 to 550 meters) above sea level.