This first-cycle large gull was photographed at Brownsville Landfill, Cameron county, Texas on February 07, 2015, and has many (all?) features of Vega Gull (larus [vegae] argentatus).
For comparison here is a similar bird from Texas in March 2008.
UPDATE Feb 13, 2020: Here is a link to a very similar bird from Japan in early April.
UPDATE Feb 13, 2020: Here is another link to a different but similar bird from Japan in early April.
UPDATE Feb 13, 2020: Here is yet another link to another different but similar bird from Japan in early April.
For comparison here is a similar bird found by Alvaro Jaramillo california in February 2012.
For comparison here is one sample page of first-cycle Vegas from the Ujihara's Japan Gull Site.
Compare the rump/utcs in the image below with the last image of the March 2008 gull linked-to above:
