So many bees in the garden, but why all the squash?

Today’s question: We have several redwood vegetable planters in our yard, open to the bare ground underneath. They have become home to little gray and black bees, much smaller than the typical honey bee, who swarm in large numbers, going in and out of holes they've burrowed where the wood meets the ground. From cautious experience, I've found they are not at all bothered by my presence, showing no inclination to land on or sting me, even when I'm watering. They happily go on about their business of pollinating my tomatoes and squash while I work among them. Do you know what species they could be and if they are indeed harmless?

I feel kind of bad about this one because it comes from a really smart guy who has helped me with several questions in the past and now that it is my turn, I don’t have a very good answer.

The part that throws me is the swarming thing. Most bees that behave like the ones in question are loners.

Sweat bees? The gentlemen said they don’t bother him. Sweat bees like to lick the salt off your skin.

Squash bees? There are squash involved, although why anyone would want to grow such a thing is beyond me.

I’m going to guess mining bees. Mining bees are harmless solitary creatures with individual underground burrows. They often share a communal entrance. That would explain the appearance of swarming.

After they mate, female mining bees collect pollen on the hairs of their back legs, carry it to a burrow and deposit their eggs on it. The larvae feed on the pollen.