Photo of Grand Canyon (image) GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre Share Print E-Mail Caption Photo of Grand Canyon, Colorado. The "Great Unconformity" indicates the major global surface erosion event. (public domain / pixabay.com) Credit public domain / pixabay.com Usage Restrictions None Share Print E-Mail 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.