This is a very simplified version of Snake Valley's geologic history. If you'd like more indepth information, please consult Frank DeCourten's excellent book The Broken Land: Adventures in Great Basin Geology (2003) or Lehi F. Hintze and Fitzhugh D. Davis's detailed Geology of Millard County, Utah (2003). Click here to see a geological time chart.
During the Paleozoic Era (Ancient Time), a shallow inland sea covered this area.
Sea creatures died, sank to the bottom, and over time were crushed by the weight of more creatures' carcasses pressing on them. Over millions of years, there were enough deposits to form sedimentary rocks like limestone, dolomite, and shale. Forces deep inside the earth created heat and pressure on some of these rocks, turning them into metamorphic rocks like Prospect Mountain Quartzite.
The next major time period, called the Mesozoic Era (Age of Dinosaurs) began. After the sea dried up, a series of sandstorms deposited thick layers of sand (which later eroded away from Snake Valley but can still be seen in places like Zion National Park). In addition, rock from within the earth was extruded in the form of granite. Still, the land was virtually flat until a series of earth movements, caused by the Farallon plate crashing into the North American plate along the West Coast, buckled the earth and moved some layers of rocks tens of miles in what is called the Sevier Orogeny.
Snake Valley still didn't have major mountains, but it had some topographical relief, and streams and rivers transported sediment and carved channels at the beginning of the Cenozoic Era (Recent Time).
Temperatures cooled and less precipitation fell, and forests covered much of Snake Valley. Starting about 17 million years ago, during the Miocene epoch, the earth's crust started stretching, causing the Basin and Range Province to be born. Parallel mountain ranges, with deep basins between them, were formed, and a regional uplift raised the elevation from just above sea level to about 5,000 feet.
Beginning 1.8 million years ago during the Pleistocene epoch, the climate varied between cool, wet glacial periods and hot, dry interglacial periods. Over the last 800,000 years, at least 15 of these climate fluctuations occurred. Although massive ice sheets moved south from Canada, none ever reached Snake Valley. Glaciers were present in the Snake and Deep Creek Ranges, as evidenced by the glacially-carved cirques and rock moraines that they left behind.
About 25,000 years ago,
a lake began forming, and over time it covered as much land as today's Lake Michigan. This lake, Lake Bonneville, had an extension that filled most of Snake Valley. The lake had several periods of fluctuations, leaving behind huge terraces that can be seen at the north end of Snake Valley. By about 11,000 years ago, Lake Bonneville had shrunk to approximately the size of the Great Salt Lake, a remnant of the former huge lake.
The principal geologic forces still acting on Snake Valley today are the continued stretching of the Basin and Range Province, which can cause unpredictable earthquakes, and erosion.