After a recent rain mounds of very small black bugs have appeared

Question

Rained last night after about a month or so of no rain. Bugs appeared at the base of a playhouse, rock wall, exterior house wall (brick), scraps of wood leaning against the rockwall, and in a line on the cement of the driveway about a foot from a rockwall. Almost looks like a pile of gunpowder or grit when you first see them.
The bugs are about 1/16 to 1/8 inch long.

Answer 1

They sounds like mites, but I am not sure on the behavior. I personally have not seen mites do that, but I am not an expert on bugs. I would recommend contacting this site:
http://www.whatsthatbug.com/

They may be better able to help you.