J.E. Picconi, from the Paleontogical Research Institution, has a nice website that describes the geology of the different regions of the U.S..
The site has a nice clean design, and is readable to anyone with a basic grasp of geology and geologic time.
I’ve looked at the the section on the southeastern U.S., which even a section on the different, official state fossils.
I particularly like the icons they use to show the environments in which the different fossilized organisms once lived.