Beyond the Alaska Peninsula and bordering the Bering Sea, extensive coastal plains are found with numerous lakes and meandering streams. Only a few mountain ranges extend as points into the sea. The Yukon River has formed a large delta with many old lobes that form a vast plain connecting small, elevated tracts. The oldest is located in the now-drowned mouth of the Kuskokwim River. One reason this coast differs from the glaciated coast of southern Alaska is because it was largely ice-free during the Pleistocene era.