Most Cretaceous sandstones are of marine origin. Terrestrial dinosaur fossil-bearing strata are usually siltstones, mudstones, fossilized volcanic ash, etc.
This area appears to have been alluvial flood plain from a map I pulled up. I was amazed touring the area how much of the sandstone was aoelian. I guessed Dakota because it does have silt and mud interbeds from a strat column I pulled up.