Darkling beetles (Coleoptera: Tenebrionidae) make up a large and diverse group of insects, with over 1000 known species in North America alone. Over 20,000 are known throughout the world, and species vary considerably in appearance. I suspect the individual shown here is of the genus Asidopsis, possibly A. opaca.
Although they occur across most of the continent, darkling beetles are particularly common in the west. Many are adapted to arid and semi-arid conditions, and these beetles fill the ecological niche that is occupied by ground beetles (Coleoptera: Carabidae) in areas with more moisture.
Darkling beetles are usually encountered on the ground or under rocks, logs, or bark. The Latin name for this family means “lover of darkness” and these insects often remain out of view, scavenging for food. A few species are known to feed on decaying animals, dung, and fungi, but in general most feed on plant material. Some are also pests of stored grain.