black-throated green question, allegan

[Caitiln Woods]

I was at Allegan State Game Area this morning and I saw what looked like 
a black throated green, only it had a black cheek.  In Sibley's this 
most closely resembled a Townsend's Warbler, but I'm guessing that this 
is not the case.  Is there anything else I could have mistaken it for?  
I did not get a very good look.  It was with a group of yellow rumped 
warblers and perching rather low.

Caitlin