Features on the surface of Earth provide evidence of past events as well as ongoing processes in our planet's geologic history. Sometimes the ongoing processes uncover evidence of events in the more distant past. For example, as the Colorado River carved out the Grand Canyon, it uncovered 400-million-year-old rocks and exposed evidence of ocean advances and retreats, as well as the history of plant and animal evolution during that time. However, ongoing processes may also destroy evidence of past events, eroding or otherwise transforming geological features and making the task of unraveling geologic history a difficult one.

Like countless regions of the world, the area surrounding Lake Mead, Nevada, has been the scene of a multitude of geologic events. For example, there is evidence that about 2 billion years ago this area formed the western coast of North America. Subsequently, the continent collided with and connected to a volcanic island chain, was flooded several times by inland seas, experienced numerous periods of uplift and erosion, and joined with other continents to form Pangaea, before breaking apart again.

Despite all these events, the geological events of the past 18 million years are the ones that have most clearly defined the region. During this time, movement of Earth's tectonic plates caused explosive volcanic eruptions. At times, this activity blanketed the area with ash, debris, and lava flows. The movement of tectonic plates also stretched the continental crust, causing fault lines to open and the land to break into tipped block formations with high peaks and low valleys. What's more, scientific evidence suggests that this area of stretched crust, called a rift zone, continues to pull apart today. If so, the area around Lake Mead, a human-made reservoir, may one day be the site of a natural inland sea and the boundary between two diverging continents.

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