Saturday, June 16, at 9:00 a.m.: Karst Geology Walk at Thacher Park. Much of the rock found in Thacher Park is limestone. Limestone can be dissolved through natural processes, giving rise to topography called karst. Features of karst topography include sinkholes and caves. On this walk, we will see some fine examples of karst and learn about a process that is shaping the park we see today. Call 518-872-0800 to register and for meeting place. Park entrance fee is $6 per vehicle.