You probably came to this location because of the nearby geocache of historical signifigance. While you are here you might as well learn a little something about geology, right?
If you look at the boulders at this location at this location and at the upward slope, it appears to be stained, or painted by flows of something running down the surface. It can also form on the sides where water never really would get to the stone in rain or snowfall. Sometimes minerals within the surface will form the varnish, and other times windborn sands/clay particles will be deposited on those surfaces.
For decades the prevailing theory is that the varnish is formed by micoorganisms that take those minerals out of the environment and they get cemented onto the rock surface. Causing the rust to form (black rust for the mineral manganese) and running down the surfaces or sticking on the surfaces.
Yet a newer theory by Randall Perry of Imperial College London is breaking that idea, that it is silica that deposits on the rocks entobming the microorganisms and the varnish like amber. " The team also discovered that, just like amber that entombs ancient insects, desert varnish tends to trap fingerprints of biology, such as amino acids, DNA fragments, and even microorganisms from past eras that lived on the rocks or simply became stuck to them"
The colors of desert varnish can be reds from irons to black from manganese, then every color shade in between.
Logging tasks
- Does the desert varnish appear in streaks here or is it evenly covering the surface?
- Is the color even or varied?
- Do you have another theory as to the discoloring of the rocks?
- Looking to the opposing sides of the boulders, compare the varnish, varnish amounts, colors on the two sides.
- Post a photo of you or a proxy near this location. You should be able to see what is necessary from the road. No need to climb the hill.
References
Desert Varnish by the National Park service
Dorn RI, Oberlander TM (1982) Rock varnish. Progress in Physical Geography 6:317-366
Liu T, Broecker W (2000) How fast does rock varnish grow
https://www.sciencemag.org/news/2006/07/solving-mystery-desert-varnish