Johnette Napolitano is amazing. I know her original band, Concrete Blonde, isn't strictly Americana. You could make a case that they followed in the LA music that produced the Blasters, X and otheres.
She tours by herself with an acoustic guitar with old songs a little flamenco thrown in. When her voice is low it can be husky, deep and rich. She does have a pretty unique ability to take it up to levels that can tear off the roof. What makes it amazing is that as she moves up it gets purer and more on the note.
I love Johnette's voice. Totally agree - been listening to some old Concrete Blonde stuff lately actually, and kinda thinking the same thing. What a voice! I think Linda Perry from the confusingly similar 4 Non Blondes maybe sounds a little like her too, but I prefer Johnette.