Hello FF.
Thank you for your thoughtful and informative reply. The geographical research for the novel was especially interesting, given that it is set well before the Louisiana Purchase, so I had to acquaint myself with French America as well as Spanish America. And the question of exactly which territory constituted the plains did indeed present itself. I consulted lots of period maps but was unfamiliar with the excellent source you provided. The Harvey Leifert link is hugely interesting in its own right and full of valuable information. The maps are beautiful and I would recommend them to any other readers of this forum who have an interest in American history. I wasn't familiar with Walter Prescott Webb either, but the link you provided is fascinating and touches closely on the concerns raised in the novel. I have bookmarked both sources for further reading and research. Thank you again for taking the time to reply and alert me to both sources. It's the kind of gold one hopes for in forums such as these but rarely receives. Much appreciated. J