Swarm at a stripmall
I live in Southern CA where it was over 80 yesterday so take that into account here.
First of all I am assuming that this was a hive that was disrupted and absconded. The swarm looks pretty large and even for this area this is pretty late for a natural swarm. Even forage in town is light and I have not seen any drones for a month or more.
I drive an old 1971 GMC pickup and always carry a hive or two in the truck. (Farmers market prop and cut-out calls). One of these was from a recent dead-out, three deeps high with all natural drawn comb the bees drew on foundationless deep frames.
On Thursday I had a need for a one-day car rental and parked my truck in the parking lot of a strip mall at 9am. I returned at 5pm and from a distance, could see a few bees around the truck.
The person at the desk asked me if that was my truck and began to excitedly tell me about the huge swarm that filled the area and were "all over your truck". Outside the rental office (it is in a strip mall in a very built up residential/business area) the real estate, nail place and bookshop people all came out to tell me of the sight.
I calmly walked over to the truck and they were indeed bees lined at the front of hive fanning. The hive was humming and I did not see any more bees flying. Blocked off the entrance and after telling the people what had happened and why, they all were happy the bees would bee cared for.
They then went to a poker game till 12am and then home. Took the hive out at 6am Friday and added some brood and stores.
Luck day all around...
"When in doubt, empty the magazine."