Footprints of Thunder — James F. David

When a freak natural phenomenon dissolves the boundaries between yesterday and today, the world is transformed into a patchwork mixture of the present and the distant past. Entire cities are replaced by primeval forests. Prehistoric monsters stalk modern city streets, hunting for human prey.

While ordinary men and women struggle to survive in this strange new world, the president and his advisers search for a way to undo the catastrophe. But the solution may be more devastating than the dinosaurs....