Chihuahuan Raven is a species of dry Southwest grasslands occupying lower elevation habitats in places where it overlaps with Common Raven.
Chihuahuan Raven is distinguished from the Common Raven by habitat, smaller size, shorter bill, longer nasal bristles (feathers coming down across the upper ridge of the bill) and voice (Chihuahuan Raven's call is higher pitched and sounds more like a mallard call).
The two raven species should be distinguished with care in areas of range overlap, such as in Texas, Arizona and New Mexico.
The Chihuahuan Raven tends to be found in more open habitats at lower elevations, not in mountains or forests (although the Common raven can be found in low grasslands, too). 
The often mentioned white-based neck feathers of Chihuahuan can be hard to see, but this can be a good field mark if the wind is blowing the right way!

Big Bend National Park, Texas, USA, 12 April 2007