Telltale Ridges (IMAGE) Columbia Climate School Caption Digital elevation map of sediment strata formed on a lake bottom some 220 million years ago, near present day Flemington, N.J. The lakebed was later tilted so that its cross section now faces the sky. Purple sections are ridges -- remains of hard, compressed sediments formed when climate was wet and the lake deep; alternating greenish sections are lower areas made of eroded-out softer sediments from dryer times. Each pair represents 405,000 years. Groups of ridges in lower part of image manifest a separate 1.7 million-year cycle that has today grown to 2.4 million years. Thee 40-square-mile area is dissected by parts of the modern Raritan and Neshanic rivers (blue). Credit LIDAR image, US Geological Survey; digital colorization by Paul Olsen Usage Restrictions Credit must be given. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.