The effectiveness of a computer application depends on, among other things, an efficient user interface. In order to visualize subsurface geologic phenomena using the Google Earth™ application, we initially employed the built-in Google Earth time slider. Dragging the slider's right thumb elevated a COLLADA model that initially loads at a subsurface altitude. However, the double-thumb feature of the time slide caused users some difficulties. It is not possible to turn off this feature when not required, so it can be misleading to users. Because of this and because of the need for more control, we transitioned from the stand-alone Google Earth application to the web-based Google Earth plug-in. To overcome some of the limitation for the existing user interface, such as the inability to make controls appear semitransparent, we designed and implemented a screen overlay using the plug-in's application programming interface. This approach opened new possibilities to build more customizable user interfaces. A demonstration of the approach and sample usage of JavaScript to create buttons, draggable images, slides, and slider controls is presented.