The note can be found in a duffle bag during the Free States Loner random encounter.
I turned on the faucet the other day and out came this dirty, gray mess. Then I get to find out that not only is the water purifier busted, but my air purifier's gone to hell, too. These damn vines managed to find their way through a concrete wall and right into the machinery. They're so unnatural, I don't even want to think of what sort of "government experiment gone wrong" this is.
Now this just means, I can't stay here. I thought about holing up with the others, but rumor is some of them want to help the survivors out there. Bunch of crazies. Those very survivors are the ones that ridiculed us. They killed Caleb's family. I even found two dead bodies outside my own bunker trying to break in.
I'm just going to take what I have and head west.