Metamorphic Core Complex

The North and South Snake Ranges are metamorphic core complexes, meaning that the core of the mountain range consists of metamorphic rocks that have been uplifted. The overlying sedimentary rocks have for the most part eroded away, leaving the older rocks exposed. A fault along which some of this uplift occurred is exposed in this area and is called the Northern Snake Range Decollement. This low angle fault can be seen along the canyon walls and on The Table of the North Snake Range.


Cave Geology
The caves in Snake Valley are formed in limestone and dolomite. The cave forming process is one of dissolution. Water and carbon dioxide mixed as they entered cracks in the ground, forming carbonic acid, which slowly dissolved away the sedimentary rock. The water was supplied by the water table, but when it dropped, the dissolution process stopped. Then it became time for the cave to fill up with cave formations. Water from snow and rain still seeped into cracks and entered the cave, picking up carbon dioxide as it passed through organic material, but when the carbonic acid reached the air in the cave, the process reversed, with the carbon dioxide being released to the air. The water, infused with a little bit of the limestone it had dissolved on the way down, deposited that limestone in the form of calcium carbonate. The flow path of the water determined if the calcium carbonate was made into a stalactite, stalagmite, soda straw, drapery, or other cave speleothem.

Geology
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.