How large is the piece? There are some very hard woods that grow in desert areas, like the central Washington basin, or Utah/Nevada, but they would not get very big. 6-7" would be large for one of these. Mountain Mahogany would be one, though the species that grows in our area doesn't really look like what you've got. Anybody know what Salt Cedar looks like?
The dulling effect could be related to silica in the wood, rather than the hardness of the wood. Silica would correspond to growing in a desert environment, so consider a Rocky Mountain Juniper equivalent, that somehow got discolored. (checking the color/odor under the brown surface would be useful)
In the Tri-cities/Yakima areas, some sort of fruit or edible nut wood is always possible, though what you have doesn't look like any with which I'm familiar.
Last thing to consider is that it got burned. If there was a wildfire and whatever this is got rapidly toasted, it could have changed some of the wood characteristics, and that ribbed surface visible, might have been burned. (Or wind scoured.)