Replaced concrete with native soils a few years ago by moving dirt around my yard to fill the hole left by concrete slab removal. Didn't want to pay for top soil and a lawn, didn't want to water a lawn or treat any ground with herbicides and pesticides. So I put native plants in the native soil. I selected grasses and sage and a live oak species specific to my coastal zone of SoCal. Did it all myself to save a little cash.
Then this little guy (guys?) showed up. It is a mouse who lives nocturnally, feeds on native plant seeds, and at dawn digs holes like this one for a home.
I caught this one digging its hole last week. (It's not in the pic, obviously.) Turns out it is an endangered Pacific Pocket Mouse native to my immediate micro-climate. It was thought extinct until 15 or 20 years ago. Now a university in San Diego has a program of reviving the species. They have been releasing lab-bred mice into the wild.
One of 'em found my native yard this summer. Way damned cool.