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The Supercontinent Pangaea started splitting apart in Triassic time. By Early Jurassic time (about 190 million years ago) rifting separated West Africa and the Eastern U.S. and began opening the Atlantic Ocean. By Early Cretaceous (about 120 million years ago) Africa separated from South America; and by Late Cretaceous (about 80 million years ago) North America separated from Greenland. Each of these events affected the direction and velocity of the plates, the rate of convergence, and the tectonics in the western U.S. (and in Montana).
The animation program at the University of Pittsburgh covers the last 270 million years. [Caution! The images may take up to 5 minute to load. Choose the "Forward in Time (270 Ma to 0 Ma)" option.] The animation conveys very vividly the many changes in the motions of the plates.
The German GEOMAR website has several useful plate tectonic reconstruction programs for the last 150 million years. They have an animation of continental drift that is much quicker to load than the one linked in the previous paragraph. Maps showing the position of the continents can be generated for any time in the last 150 million years in 5 million year intervals. Particularly useful is the option of displaying magnetic stripes on the ocean floor. For the plate tectonic enthusiast the following set of parameters will generate your own set of maps for the U.S.
Age to be Reconstructed: 80.0
Move Plates Relative to: Hot Spot Ref. Frame 1
Boundaries: North 70.0, West -140.0, East -20.0, South 10.0
Annotation Interval: 20.0
Gridline Interval: 10.0
Map Projection: Orthographic
Frame Type: Thin Lines
Outline of Plate Fragments: (checkmark) Black
Colored Plate Fragments: (checkmark) Ochre
Magnetic Lineations: (checkmark)
Present Day Shorelines: (checkmark) Red
DSDP Site (red): (checkmark)
ODP Site (green): (checkmark)
Generate the map and then either print it directly from your browser or download the file in TIFF format and print it later. Change the age from 150 million years to 140 million years and print the next map. With a bit of effort you can have a set of maps from 0 to 150 million years at 10 m.y. intervals. The Hammer Projection is also useful. Hot spots move very, very slowly compared with the motion of the plates. Thus, the hot spot frame of reference gives "absolute motions"
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Plate Tectonics of Montana (Page 8 of 14)