This gnaphosid readily keyed to Gnaphosa sericata. I saw a bright red critter running across a sparse caliche meadow, in full sun, and my brain instantly thought "mutillid." Looking closely, I saw it was a gnaphosid. I snagged it and brought it home for a photo-shoot. Inside my house it's color became a very dark red. This critter appears bright red in the sun and dark red in the shade. I used photoshop to create images of the spider in both colors. They differ only in the "color correction" value of the shadows/highlights dialog. Curiously, the specimen Kevin Pfieiffer posted is brown rather than red: