Hi Sheldon,

It is interesting that some areas of you lawn seem to be fine, but other parts are dead.  Was something washed onto your lawn?  Is the soil under the green areas difference from the dead areas (i.e. less sand and more moisture).  

The first thing that I would do is get a soil test to see if there are any issues with pH, EC (salinity), or nutrients.  OSU has a soil health lab where you can send soil sample for analysis, I would recommend the standard soil test for Eastern Oregon. 

You could also rule out insect damage by digging you a 1 square foot area to a 1-2 inch depth and examine the soil for insect larvae.  You'll want to do this on the margin of healthy grass and dead grass.  This is where the insect will be feeding.  

If everything checks out with the soil test and no insect, then I suspect the sandy soils are causing the issue.  Most likely, the soil can not hold enough moisture to support the grass.  You may want to consider incorporating compost or some type of organic matter to the soil prior to reseeding, to improve moisture holding in the soil.   

Chas