Geology in the Parks home NPS home USGS home National Park Service/US Geological Survey banner
Mojave title bar
Click to see map showing field trip stops Cima Dome title
Individual grains of feldspar lie surrounded by soil.  The minerals surrounding these large crystals have weathered to form clays, leaving more resistant feldspars behind.
Individual grains of feldspar lie surrounded by soil. The minerals surrounding these large crystals have weathered to form clays, leaving more resistant feldspars behind.

 

Nibbling away the mountain

Once at the surface, granite falls victim to the slow, gnawing forces ofweathering and erosion. Water falling on the rock as rain or snow and groundwater percolating just beneath the surface begins to disintegrate the rock grain by grain.
spacer image Water and dust particles gradually work their way between individual mineral grains. Mica and feldspar grains in the granitic rock chemically react with the water and decompose to form clay minerals. Clay minerals and dust tend to swell-up when they get wet, then shrink when they dry out. These tiny particles act as wedges between more chemically resistant minerals, prying them loose from the solid rock, like the potassium feldspar grains in the image on the right. Over time, the granite ‘rots’ and streams begin to carry away the loose, rotten granitic soil.
Notice the bumpy crystals of feldspar protruding from the granitic boulder in the foreground.
Notice the bumpy crystals of feldspar protruding from the granitic boulder in the foreground.
Eventually, the mountain retreats back, leaving a gently sloping surface behind. Over millions of years mountains can retreat so that just a few exposed boulders remain, like those you see on the top of Cima Dome.
buttonView geologic map of area (large files!)
On to the Granite Mountains

Back to field trip menu


| Mojave geology home | Mojave National Preserve home |
| Locate Mojave | Mojave geology field trip | Education resources | Geologist’s page |
Mojave horizontal bar
| USGS Geology in the Parks home | NPS Park Geology Tour home |

This site is a cooperative project of the
US Geological Survey Western Earth Surface Processes Team
and the National Park Service.

Please share your comments and suggestions with us!
parkgeology@den.nps.gov
http://www.nature.nps.gov/grd/usgsnps/mojave/cima2.html
This page was last updated 3/24/99