TThe Jurassic period of the Mesozoic left discoverable rocks in NW Minnesota, known as the Hallock red beds. They are known from drill holes and do not contain fossils. Nearby evaporites in ND and Manitoba suggest that the climate was hot and semi-arid. It is likely that dinosaurs wandered across Minnesota but no remains have been found.
The Jurassic was followed by the Cretaceous when the seas advanced upon North America. The eastern shore of this Cretaceous sea was located in part of MN. Sediment deposited in this sea was mostly siltstone. Conglomerates made up of hematite pebbles are found, which indicates that the hematite must have been formed quite some time before it was weathered and broken up. The entire world most likely experienced warm climate.
Some coal has been found in Minnesota from this time, made up of conifers. It is likely the landscape was swampy. Weathered granites and gneises have left behind kaolinite, which is used in ceramics.
Dinosaur remains in Minnesota may lie under glacial drift. A few cretaceous fossils have been found, including a marine crocodile, sharks teeth, ammonites and snails. Also the variety of plants include flowers, ferns, conifers and deciduous trees.