The geographic feature that formed the eastern boundary of the thirteen American colonies was the Atlantic Ocean. That geographic feature still forms the eastern boundary of the continental United States. As boundaries go, the Atlantic Ocean is a very good boundary to have. It provides all kinds of natural resources, which was useful for the colonists. Food would be a good example: the fishing grounds that exist in that part of the world are among the best. Being right on the Atlantic Ocean also gave the colonies easy access to various trade routes with multiple countries. This allowed the colonies to develop as powerful import and export hubs due to water access through many harbors. The booming trade industry helped establish and maintain jobs and supported the economy. The British recognized the importance of this boundary, which is why they tried to blockade much of it during the American revolution.