And I forgot the link:

http://www.mccutchentrace.org/yard/photo(4).JPG

Yes, that is a dahlia. I don't know the specific name of it but it is probably one of the bb size. This fall would be a good time to divide it. If it has been in place for many years you might need to just chop it in quarters with an ax and them remove all the damaged pieces. You will still have many tubers left to replant, or you can replant one of the quarters and share the others or plant them elsewhere. You might enjoy adding some other colored dahlias to complement it :-)