Dark Winged Fungus Gnat
Sciaridae -- Dark Winged Fungus Gnat Family
Fungus Gnats (many species) are rarely more than 3 mm in length. They are very common around soils that have high organic content. The minute larvae tunnel through moldy vegetation where they are important decomposers and recyclers. In the Sonoran Desert they would be encountered near damp and shady soils at springs.
Occasionally homeowners will find them indoors because they can thrive in the soil of potted plants - particularly when over-watered. On rare occasions they will become over-abundant in the soil and begin nipping at the plant roots. If you maintain a compost heap, they will be among the abundant insects tunneling and flying nearby.