Location is along Highway 16 (Jackson Highway) at the Folsom South Canal, just west of the junction of Hwy 16 and Sunrise Blvd, Sacramento County. The birds are nesting in bull (milk) thistle in a mining pit about 50 m west of the Folsom South Canal. The birds are going to the canal to drink and are collecting nesting material near the fence and trail there.
I checked 135 birds for bands, of which only 8 were males. I saw two banded birds, both with bands on their left tarsa. The first was seen at a distance through binoculars only, and appeared to be a white band. I saw it only briefly, but was confident that it was a pure white band (not reflection of the tarsa). Subsequently, with a scope from a close distance (<30 m), I saw another female with only a USGS silver band only - no color band. The presence of the silver band made me wonder a bit whether the band on the first bird was also silver, but I don't think so.
At least 5 females were collecting nesting material and going to the patches of bull thistle. The birds were streaming back and forth from lands to the north. I counted up to 300 birds in the air at one time, so estimated a likely minimum of 500 pairs, but possibly a lot more, though the habitat is limited.
There was excavation equipment in the immediate area, but the mature bull thistle indicates no recent disturbance of the nesting substrate.