From the ebook map*map*, Underhill, the first settlement, is located at approximately
latitude 8.05 degrees, longitude -43.9 degrees, or about here:
For comparison, the location proposed by the Red, Green & Blue Mars Site is approximately where the small white X is, above the Hebes label (latitude 3.864254, longitude -69.345703 as suggested in the comments to the accepted answer).
On the planetary scale that, the e-book version is about where the large blue pin with the star is located, and the RG&B Mars site's location is where the small white pin is:
Ebook ISBN: 9780553898279
*Clicking on the Read a Sample button should bring up the map.