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.

On this link: http://www.birdjam.com/birdsong.php?id=63 songs 9  
through 11 on this recording match what I heard.

Thanks to all who offered their input.

Rog

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