I have recently noticed holes appearing in my yard. The first was

discovered when digging our pond. There was a perfectly round hole,

several inches in diameter, quite deep, nearly the length of a shovel

handle. It looked as if were machine made, it was smooth and perfect.

The next hole occurred near the rear of the house, a bench collapsed

into it! Today I noticed another, around the corner from the last one,

through the gravel in the side yard. I am in the middle of Los Angeles,

the only "wildlife" I have are birds, squirrels, feral cats and rats.

What could be causing these?

Thanks,

Tina