Numerous ant holes surrounded with chaff, the husks of the grass seeds they have been harvesting.

I saw five swarming ant groups and they may have all been part of the same colony since all were within a 10' radius.

Correction on the ID: It was not Messor. Under glass this had head and gastor black and a brown/orange rounded thorax and one petiole, 8-10mm as per: California Academy of Sciences Identification Key to 16 Common Ants of The San Francisco Bay Area.