It's just the Northeast of the US: NYT, WSJ, Washington Post; and of course NY is the center of journalism (as with many things), and Washington and NY are the leading centers of power and therefore news. There are no equivalent west coast or southeast news sources.
However, don't forget that the largest 'publication', or publisher, is Murdoch: Fox, Wall Street Journal, etc. And that is right-wing and the most biased.
The influence of the coasts has been remarked on for a long time, but I think with the Internet it's actually a much improved situation: People easily get news from all over the country and the world. Everyone can read the BBC and much more (including Russian sources, without even knowing it! :) ), and they also get their news, for good or ill, from random people worldwide! :P
> journalists for the largest publications are overwhelmingly far more left-wing than the rest of the country
That assumes the personal political beliefs have a large effect on their jobs.