These pics were taken on February 01, 2006 at an East Houston, Texas landfill; the default ID for a bird like this is LBBG, but the bill looks unusually strong, bulbous and hook-tipped, and the general structure suggests something with a stronger build, like Yellow-legged Gull or even Kelp Gull (on which the upperparts can be mid-gray rather than black in intermediate plumages, in the South American population):
