Whoa! I just realized this thread is over a year old now!

(Just felt like mentioning that. *shrugs*)
If you want to think about this scientifically (as far as the dinosaurs’ ranges are concerned), then it would make the most sense for the Great Valley to be located in either Laramidia or the northwestern part of Appalachia (in what is now central Canada), as the vast majorityóif not the entiretyóof the North American dinosaurs in the series are only known from fossils found west of the Mississippi.
One potential problem is that, judging by the map, northwestern Appalachia is not very mountainous, and mountains are a prominent geographical feature in LBT. Laramidia, meanwhile, looks almost TOO mountainous. Also, since the climate was much warmer then, the Great Valley would have to be located quite far north if it were to receive snow, and northern Laramidia looks a little too narrow to me.
Personally, I think it would be more realistic for the LBT series to take place either before or after the period to which this map dates, perhaps when the Western Interior Seaway was less extensive.