What winged insect is in this photo? Is it Axymyia furcata?
Great pictures.  First, fly or wasp?  

In the second picture, under the head you don't see jaws of a wasp, but do see a bit of a tongue-like organ, like a fly.  Further down, you can see that there are only 2 wings.  Just below where the left wing meets the thorax, you can see what looks like a tiny wing or paddle.  That's a haltere, a reduced wing that vibrates to provide stability, like a gyroscope.  Flys have halteres.  Finally, in the first picture at the very end of the abdomen are 2 points.  That ain't a stinger, it's an ovipositor.  It's a fly, female, and from the size of the abdomen, gravid.  

The closest I've gotten to identifying this one is Axymyia furcata http://bugguide.net/node/view/1216479.  Everything matches, as well as we can see from a photo, except the coloration.  Also, A furcata is associated with streams and is found in the north-east and north-central US, while, your bug was found on a lawn in CA.  For more information about A. furcata than you need, there is a master's thesis available:  http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1882&amp;context=etd.

I've looked at hundreds of fly pics to find the one I linked to above.  That's the only fly I found that matches the shape of yours.  Maybe it's a different fly within that genus, maybe it's just a color variation.  

Their maggots live in rotten wood and decaying plant material, and the adults are mostly interested in more maggots, so this isn't a pest, just a neighbor.  

Edit: furicata --> furcata, oops.