1. Putative Iceland (juv)
2. Thayer's (adult) (or maybe Iceland; Kumlien's Iceland can sometimes show this much dark gray on the wingtip)
3. California (center, lower left, and upper right)
4. American Herring (pink legs) - lower right and upper left
5. Ring-billed (center, facing left)
I believe the pale California Gull in the front center is the larger, paler-mantled "albertaensis" subspecies of California Gull.