Immature Gulls

There were quite a few Gulls around the Bow River at Pearce Estate this morning. I don't know much about Gulls, so won't even attempt to identify these juveniles. I think they are quite attractive with their brown mottling. Hey, Nancy - hope you got some good photos! Mine were a bit disappointing, apart from maybe three or four of the 29 pictures I took (no, Doug, it wasn't 100!). Maybe immature California Gulls?? Or Ring-billed?