Soil and Rocks
I need to jump ahead here a little and put my travels into perspective (geological). The earth we mostly deal with consists of soils with different properties, like the hard, dry sandy soil we dug in for arrowheads in SW Colorado. This soil is the eventual product from weathering of rocks by wind and rain, ice, plants and animals, naturally occurring chemicals, and collisions between particles in moving water. These soils are very important to engineers and farmers because we use them for everything we do. However, they do not tell us about the distant past, e.g., the oldest soil in Africa is ~55 million years, but that is really unusual…more water means younger soils. In my travels, I am interested in soils but being a geologist, I really like old rocks!
A geologic map shows rocks as if the soil were all removed (i.e. outcrops), like removing the sand from the plaster fossils at a children’s museum. The map below thus shows sedimentary, igneous, and metamorphic rocks but no sand, gravel, etc. However, the transition from a soil to a rock is gradational and Pleistocene (~2.6 million to 11000 years) rocks are often poorly lithified, as found all over Florida beneath the surficial Holocene (<11000 years)sediments. Geologic maps present these at the top of their legends as Recent or Holocene sediments. Of course, there are brand new volcanics in Hawaii and Iceland, and at the sea floor, that are quite hard (lithified); we have to be flexible in dealing with natural materials.
This geological map was produced by the USGS. It will be used in this blog to describe the areas I am discussing. There are many databases but this image shows an easy one to access for non-expert users (http://maps.ngmdb.us/dataviewer/).
The map above only shows the general distribution of rock type, which could be determined by anyone with no modern analytical methods, i.e., no dates are given. This is what I noticed while driving around (and clambering over) the western U.S., which in many ways resembles a geologic map in having rock exposures that closely follow the outcrop pattern on the map. As this page evolves, I will discuss ages more but mostly in general terms. These ideas are readily seen at the USGS dataviewer by switching between Bedrock to Surficial active layers on the Layers menu. A more complex but fun site by the US Government is found at: http://nationalmap.gov/
Geology and Offroading?
This first post hopefully explains why I want to create this page by briefly describing how I came to enjoy travel, off-roading, and geology, which occurred in that order.
My family travelled around the U.S. when I was young in mostly vintage Plymouths and a 1955 Chevy pickup. We travelled around Arizona a bit on the usual camping trips and such, and made longer-lasting and more distant journeys to Mississippi and even northern California. Needless to say, these family journeys entailed many stops for restrooms, eating, repairing the vehicles, directions, etc. And the roads were not too good either. I spent my time looking out the window at a variety of geologic features, not so much with an interest in nature, but out of boredom because this was the era before Nintendo and there were usually four of us kids packed in the rear seat, or back of the pickup (yup, no seatbelts). But we are what we do and I stared at mountains, rocks, gullies, and other geological and geomorphological features for hours on end.
The 1957 Plymouth we used for some of our family journeys.
We spent family time examining the earth for tiny objects, usually arrowheads and other artifacts in the Four-Corners area of the SW. This training would be handy when seeking small fossils and other evidence of geological history later in life.
Timothy R. Keen 
Recent Comments