The song I heard I believe to be a Cerulean Warbler. I heard it again
late morning in the Lower Campground of Garvin Park near the Host Cap
site up high in the trees. Didn't see it, but have ruled out other
helpful suggestions such as Towhee, goldfinch, and Redstart. The song
is has a slight buzz to it, but is more clear than what I recalled
Cerulean to be. Will try to monitor the site and get a visual
confirmation.