A tor is a hill or mound of bare rock that rises high
above the surrounding area. Two tors can be see to the south
of the road. These two mounds of granite appear to stick
straight up from the relatively flat desert floor. Some of the
classic examples of tors are in the moors of the British
Isles.
Tors are thought to form under thick soil. During the last ice
age, this area was cooler and wetter than today. At that time there
was a thick layer of soil with vegetation covering these. Chemical
weathering by slightly acidic groundwater broke up the
jointed granite beneath the surface into gravel and sand.
When the climate changed to the arid desert that it is today,
the vegetation changed and the soil began to be eroded away. What
little rain fell, stripped away the soil that was above the granite
and the weathered gravel and sand. This left relatively unweathered
granite cores to stick up above the ever lowering ground
surface.
Logging requirements:
Send me a note with :
- The text "GCZ5XV Tor – Joshua Tree NP" on the first line
- The number of people in your group.
- Investigate the base of the Tor. What evidence is there to
indicate if the Tor is getting taller due to erosion of the desert
floor or if the Tor is getting shorter from erosion on its
surface.
The following sources were used to generate this
cache:
- Trent, D.D. & Richard W.
Hazlett, Joshua Tree National Park Geology, Joshua Tree National
Park Association, 2002
- About.com, Tor,
http://geology.about.com/library/bl/images/bltor.htm
Placement approved by the
Joshua Tree National Park