One of the challenges involved in learning earth science is the visualization of landscapes and water flow over large spatial scales, particularly from 2D perspectives like topographic maps. In an effort to improve the interpretation of landscape features and surficial water features like watersheds from a standard topographic map, the University of Wyoming Geological Museum installed an interactive 3D exhibit called the Augmented Reality Sandbox. The hands-on Augmented Reality Sandbox allows students to create topographic models by shaping real sand and a color elevation map and contour lines that match the sand topography are projected onto the sand. Virtual rain can then be created as a blue visualization projected onto the sand when holding an object (such as a hand) that is sensed at a particular height above the sand surface. Digital rain will then flow in real time across the topographic model according to the configuration of the sand (flow is simulated based on a depth-integrated version of the Navier-Stokes equations). A collaborative group between the University of California-Berkley and the University of California-David originally developed the Augmented Reality Sandbox. The blueprints and software to build the sandbox are feely available online (http://3dh20.org/71/) under the GNU General Public License, together with an installation guide and help forum.