The shallow underwater plain that is a Continent's real outer edge. The continental shelf slants from the shore's low-tide line to the continental slope, a cliff that plunges abruptly to the deep Ocean floor. The shelf can be a few miles wide to over 200 miles (322 km), reaching a typical depth of 450 feet (137 m). It collects most of the sand, silts and other sediments that rivers carry to the sea. The eastern continental shelf of the United States is over threetimes as wide as that on the West Coast.