September GSA Today Cover Image (image) Geological Society of America Caption Iron-rich silcrete mantles beveled quartzite in south-central South Africa. Deep valleys dissect the landscape and steep hillslopes separate the valley bottoms from the flat, gently sloping pediments. Credit Paul Bierman and GSA Today. Usage Restrictions Credit Paul Bierman and GSA Today. 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.