Raised bump, no bite felt, halo with bruise.

Five days ago about a 1 mm diameter raised red mark appeared on my inside forearm; I did not feel a bite at all.  Since then, there has been a 6 mm radius circle of clear skin surrounded by a bruise halo up to 2 cm outer diameter.  No pain at all, anywhere.  The bruise appears to be lessening.  I moved three weeks ago to this area, Los Angeles region, 1/4 mile downwind from horse stables, 1/2 mile from a river.  No unusual insects seen, in fact, very few insects seen.

 Any ideas?  Thanks!