Hello, 
I don't have a field guide but am fairly certain there is a Black-headed Gull at Paper Mill Flats. This is bird I have never actually seen and is close to Ring-billed Gull sized but with a raspy call that clued me in: 
 
I was able to get this photo loaded via mobile broadband: 
 
http://www.flickr.com/photos/thrasher72/5244647646/ 
 
If I am wrong please let me know. Wanted to get the word out... 
 
Jon Corcoran