City of Rocks Earthcaching
Many of the Inselbergs, or isolated rock outcrops, which are very characteristic of the rock features of the Reserve, have case hardened crusts on the upper parts of the pinnacles and domes of the area. However the lower parts of the outcrops tend show less case hardening, or none at all, leaving friable rock surfaces which flake and blister, made up of small exfoliations.
Since well developed flared slopes, which can be easily seen on the Southern flank of Kaiser Helmet, are present on the most recently exhumed surfaces along the bases of inselbergs, they are thought to develop subsurface and are later exposed by erosion of the regolith. It is thought that the concavity that you are seeing on the Kaiser Helmet and other formations in the City of Rocks, is thought to the be the result of subsurface weathering, which is more effective where the rock is in contact with seasonally saturated regolith (i.e. dry hot summers and cold wet winters).
The deep concavity that you can observe on the Kaiser Helmet, represents the average maximum height of the saturated regolith during the summer dry season. Above this level, the regolith is periodically dry and weathering rates are reduced. During prolonged periods of stabile climate, when the landscape is neither degrading nor aggrading, enhanced weathering in the saturated zone will gradually undermine the inselberg. If the climate changes to promote landscape degradation, the flared slope will become exposed as the regolith is eroded from the flanks of the inselberg.
This two step process, a period of prolonged landscape stability and subsurface weathering, followed by erosion and exhumation, plays a major role in the inselberg landscape of the City of Rocks.
Logging Requirements:
1. Walk to the North and West side of the Kaiser Helmet (staying on the road; no need to jump the fence). Is there a flared slope on the uphill side of the formation? Why do you think this is?
2. Which side of the rock has a steeper slope, and how do you think this would contribute to the difference?
3. Comparing the nearby formations near the posted coordinates (i.e. Chicken Rock across the road, and Camp Rock to the East), do these formations show any signs of flaring?
4. Judging from the height and angle of the flared slope on the Kaiser Helmet, do you think this process is still ongoing, or do you think the formation is in a state of getting broken down, being exposed to the elements?
References:
Etched In Stone: The Geology of City of Rocks National Reserve and Castle Rocks State Park, Idaho; Keven R. Pogue
Geologic Interpretive Trail, City of Rocks National Reserve; A self guided journey to discovering secrets in the rocks of City of Rocks, Prepared by Idaho Department of Parks and Recreation and the National Park Service.