Snow or Ross's Geese
(Chen caerulescens, Chen rossii)
It would take better birders than my wife or I to distinguish these two species, but there were a lot of these birds at the Merced Wildlife Preserve (WLP) and we were fortunate to see one major fly-up, with hundreds rising from the water, circling, and then returning. A spectacular sight! Later in the day, we returned to the Cosumnes WLP and saw the geese at sunset. Several images on this page, please scroll down.
Click here for an enlargement of the center of the above image.
Below: Part of a huge flock of snow geese near Willows, in Northern California.