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I'm sorry but not sure what you're showing. To me , the holes look like perhaps a squirrel or some other critter was digging, looking for food. Don't see anything wrong with your mulch, except it may be too thick. Sometimes thick mulch gets crusty and becomes impermeable so moisture doesn't get to plants, an undesirable situation. But if it happens , you just stir the mulch around with a rake to aerate it , easy piecey.

Looks like ground squirrel work to me. In my area, they can become major problems, destroying new seedling beds, and eating many plants. They also provide sites for rattlesnakes to hide. The good news is that they can be controlled somewhat with hav-a-hart traps or with poison peanut bait. The zinc phosphide baits (Sweeneys) are what I'd recommend since, if properly applied underground, they have little adverse impact on other critters. I actually had a limited materials license to use much more powerful and dangerous baits, and did not do so; there are too many adverse and negative impacts that could result, and they really are quite dangerous!. I have had little success with some of the underground gasser solutions marketed for these critters. I find that there is a portion of the population that is too smart for either the traps or the poison bait, but that by getting rid of some of the squirrels I have much reduced damage. Also, I think it spooks the smart squirrels to see their colleagues either trapped or dead, so they tend not to be as active in the yard, moving on to other locales. I like a piece of apple with peanut butter for bait in the traps. It is not unusual to catch several squirrels a day in a single trap if you keep on resetting it.
Renais

Thanks for your posts. Come to think of it, I have to say that I haven't seen any squirrels in my yard in the two years I've lived here, but maybe I have the smart ones who came once and moved on when they didn't find anything.

I fixed all the disturbed mulch, so I'll just wait and see if the evidence returns. I could also be like that guy in Caddyshack and put on some camouflage and camp out at midnight...

It could also be a bird ... the curved-bill thrashers around me dig holes that look a lot like that at the edges of my mulched areas.