National Geographic Sea Lion's Columbia River Expedition in the Pacific Northwest, Oregon. The Astoria Bridge as seen at sunrise from the Sea Lion. The Astoria-Megler Bridge is a continuous truss bridge that spans the mouth of the Columbia River between Astoria, Oregon and Point Ellice near Megler, Washington, in the United States. The span was the last segment of U.S. Route 101 between Olympia, Washington and Los Angeles, California. It is the longest continuous truss bridge in North America.