County Boundaries in Grads

[Brandt Maxwell]

Greetings...

I'm a new user of the Grads software, and I would like to know if
there is an easy way to display (U.S.) county boundaries in the map
background.  So far, I have mostly just gone through the Grads
tutorial, and I'm hoping this can be solved with the mpdset command
(like for state boundaries).  If the county boundaries aren't a part
of the Grads package, then would I need to load in some external file
containing counties (like a shape file--or at least a file containing
lat/lons of the boundary points)?

Thanks for any help you can provide...

Brandt Maxwell
National Weather Service
San Diego, California (USA)