These types of bees are known as "burrowing bees" and they are absolutely harmless. This type of bee is actually not social; so even though there may be more than a few of them around your property, they are solitary and not part of a "hive." The chances of you being stung by one are virtually zero. Normally I would suggest a live bee removal if there were a hive or something of that nature. But the best advice for this situation is to just sit back and enjoy nature in this case. There isn't much you can do, since there isn't a localized swarm that you can kill. In fact, the bees are actually doing you a service by aerating the lawn, which is usually something you have to pay for. And like I said, there is no chance of getting stung unless you try to grab one.

This may be off-topic here, but I got here via a Google
search on "bees digging holes in dirt." Actually, (see
photo) it's more like sandstone. When I first saw this
site in February, it was mysterious. Today I went back
and it was swarming with bees. Okay, I thought, the bees
dug the holes...but in rock? Any light shed on this would
be welcome.

that picture looks like they just adopted the holes those holes were probably formed from a river long ago or something of that nature. you didn't take a picture of the bees so i can't tell you if they were mason bees or leaf cutter bees or if they were a more aggressive variety.

If you are interested about raising gentle bees or mason bees please visit my youtube channel i have a little info on how to do it.

Here is a link that might be useful: TheItalian Garden Mason beekeeping

We also have small bees that live in the ground, in our front yard. They come out in the spring, and they seem to prefer foraging on the wild violets that are the first plants to flower here. These bees might be genus Andrena, but I am not certain. Also, we have bumblebees that live in ground nests. None of our bees are aggressive, and I have never been stung.