70-200mm, 1/2000 at f5.6, ISO 400, Focal Length 190.0mm, Metering Mode Pattern
I think this is a California Gull Larus californicus.
California Gull colonies are usually located on unvegetated islands in lakes or rivers. Sometimes colonies are on the shore, but these are subject to increased predation from mammalian carnivores.
There are several large colonies of California Gulls in the southeastern marshes, and at least 5,000 gulls nest on islands in the Columbia River. Smaller numbers nest on islands in the Snake River near Ontario, in Malheur County.