OK, I was wrong...other states are available. If you go to view maps, a list of states pops up. Also, once you get to the state you're after, you can pick the category of geography you want to search for. For example, if you're looking for structures like shoals, ledges, and/or reefs, click on bars.
There's a lot of different sites that provide topos but, this is the only one I've found that provides a search mechanism like this. When you view the specific topos, there's a red mark that appears on the structure you've accessed and the co-ordinates listed (above the topo) are for that red mark. If you're looking for other co-ordinates on that topo, just click the spot on the map you want the co-ordinates for.
Here's Danbury reef in Maine about 3/4 of a mile off-shore from Biddeford Pool.