Fly or gnat???
Than you for the images.
These are Little House Flies, Fannia canicularis, which are cl.assified as nuisance pests. They're most common during cool spring weather and will disappear as temperatures rise and the environment (garden and landscape) dries. They don't bite or spread disease
Little house flies breed in moist organic matter outdoors, among them compost piles and manures (chicken, livestock, and/or dog).
See "flies" -- http://ipm.ucanr.edu/PMG/PESTNOTES/pn7457.html. (Scroll about 1/3 down to see info about Fannia species.