When I left the Margie Cove area, I crossed over 85 on Woods Road to old US 80, actually called historic  old US 80. Apparently a regiment of Mormon soldiers built a road some 2000 miles through the area in the 1840s when the US was stealing the land from Mexico and the indigenous peoples. Anyway, I found the source of the flies. There is a huge cattle stockyard about 2 miles from Woods Road.