The Land Between Seas

It's map ti~ime.

This is an extremely preliminary map of the environs of my new story, with major land forms and climate zones sketched in.

The landforms come from ([link]), and the climate sketches come from good old-fashioned research (mostly Plants and the K-T Boundary by Nichols and Johnson and wikipedia). The climate zones are:

Teal: Frenchman formation
cypress forests

Blue: Horseshoe formation
floodplains, channels, and coal swamps
brackish estuaries

Red: Wiliston Basin/Hell Creek Formation
rivers, deltas, and swamp
mild, sub-tropical climate, palms and crocodiles

Yellow: Powder River Basin/Lance formation
warm, heavy rain

Orange: Wasach Plateau/Horn Mountain Formation
Lakes, large rivers

Purple: Denver Formation
Rainforests

Green: Raton Basin
Coal forests, silt Fluvial coastal plain, Warm sub-humid
broadleaf evergreens (jungle if not rainforest)

So moving from north to south down the west coast of the Interior Seaway, it looks like we have a spectrum of tempret-subtropical-tropical forests and swamps, very wet, with heavy rainfall. I suppose the eastern half of North America would be drier, but I don't know of any Maastrichtian fossils sites from that part of the continent.

So first of all, do I have my facts strait? Are these really the most likely environments in the right places?

Second, if I am right, what does this mean for the cultures of the descendants of our time-traveler friends ([link])? As a settled culture I'm thinking of a series of city-state colonies of a Thalassocracy based on the north coast. Think the Srivijaya Empire ([link]). These guys will have colonial city states around the Seaway, with walled trading towns on the rivers that extend into the subtropical rainforest. The inhabitants of the rainforest are nomadic hunter-gatherers, slash-and-burn agriculturalists, and the Commensals, who lash their villages to the backs of hadrosaurs and ride the herds from one end of the migration rout to the next. Think Yanomamo/Mongols.

So, any thoughts? Is all this plausible (assuming the fact of time-travelling humans settling the Maastrichtian world)?

Edit: added some formations and removed some others as anachronistic. The presence of marine deposits HERE rather than THERE tells us something about the shape of the Seaway (which could just as easily have extended north from the Gulf of Mexico but which for plot reasons I have extending south). I also added some info from Jobaria's project: [link]