We notice that your Question #0013047 is related to this Question #0012829. 

We have copied the response from #0013047 and added an additional comment below. 

your photo at https://ask2.extension.org/file.php?key=vleqzivt45vnkgj1uszornmab9pghzyy&expires=<personal data hidden>&signature=62f9fb6a83ce55defbb7562e682416e3997b69b6&id=1656513

This is a hard one for me. If the hole opening is 10-12" it could be a groundhog hole. I would fill the hole as much as possible, compress it in, and cover it with metal screening (or rocks). Then fill in and compress the rest of the depression with a good soil mix going 1-2" above the current ground level (to allow for the soil to "settle"). I would plant annuals there for 1-2 years to see if the hole reappears or sinking is more than expected. 

Another thought on why there is a hole in the area. The hole may have been from an old tree stump that rotted or was ground out, or an old tunnel from something. This may have left a cavity and settled in that area. All you can do is add additional top soil to  fill it in and let it settle.  If the hole reappears, it may be an animal. Monitor and see what happens. 

Marian