Change Over Time
The “then” image is of Death Valley in California and shows border fault mountains, valley floor sedimentary deposits, alluvial fans and shallow lakes. This rift valley is young, only 2-3 million years old, but a good representation of what our Jurassic-era rift valley may have looked like around 200 Ma (image taken looking south from Mt. Sugarloaf in South Deerfield).
The Connecticut River sedimentary basin which filled the ancient rift valley, running north from New Haven, CT to just north of the Pioneer Valley, has an average width of 17 miles and depth of up to 16,000 feet, giving the observer today an idea of the rift valley’s size and great depth.
Refer to Richard D. Little’s book, Dinosaurs, Dunes and Drifting Continents (see Resources), section on “formation of the Connecticut River Valley” for further information.