Pillows aren’t for sleeping
Size:  (not chosen)
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Traveling east or west on US160 you junction onto CO12. Before the junction onto CO12 you have wonderful views of the East Spanish Peak, the West Spanish Peak, and the Sangre de Cristos Mts. Traveling CO12 you are virtually at the base of the West Spanish Peak. South of La Veta you are up-close and personal with dikes, sills, and of course the uplifted Dakota Sandstone that you actually drive through. You can actually touch a dike. What a sight to see and enjoy! It’s a pleasure to be here.
County Road 415 off of CO12 is busy with tourist, residents, climbers, campers, or drivers taking the Forest Service road short cut to or from I-25 at Aguilar. Many people pass the road cut where the pseudo pillow basalt is seen up close and personal and never realize what they have seen. Some may pass and wonder what kind of rock that is, or make a comment that they have never seen rock that look like bubbles or pillows. There are a few who will stop at the road cut for a closer look and will promise themselves to look later in some book to explain what they saw. See Figure 1.
A few miles north of the community of Cuchara on CO12 you can see North, Middle, and South White Peaks. South White Peak is about 1.5 miles northwest of the pseudo pillow basalt. The White Peaks are a very thick sill that flowed west. It is suspected that part of the larger sill spread south and west, thinning as it flowed. A sill is magma that flows horizontally forcing itself between two rock layers and spreads the layers apart. A dike is magma that flows vertically forcing itself between several rock layers that have vertical cracks. The sills are 20-22 million years of age. The magma more than likely came from the West Spanish Peak stock.
There is evidence that the flow of magma that produced the bubbly pillow shapes stopped not too far away from where you are standing and looking at the pseudo pillow basalt. You may have noticed that the edge of the road on its west side drops straight down. Figure 2 shows the very steep drop-off at the edge of the road. Figure 3 shows the edge of the road and the angle of decent that is reducing. Figure 4 is about 60 feet below the road that shows the angle of descent leveling out to about 30 degrees as the slope descends to the to the valley bottom about 200 feet below the road.
The magma on its westward journey forcing its way through horizontal rock layers finally lost steam and stopped. The magma and toothpaste have something in common. Have you ever noticed how the toothpaste comes out of the tube like the beginning of a bubble? Ah ha! You can see how the magma produced the bubbly shapes in the basalt from a similar squeezing process. You probably noticed that the basalt bubbly shapes seem to have one or more pillow cases around it. What store do you think the magma bought pillow cases for its pillow? Sorry, no store available. The magma did it all itself.
The first magma making the bubbly magma pillow shape cooled. More magma continues to flow at tremendous pressure from its source. Sometimes it has the opportunity to flow in another direction to form other shapes. Sometimes it flows in its original direction and forces itself to flow around what had cooled, making the bubbly magma pillow case. There can be just one pillow case or several pillow cases. See Figure 5.
Why are the definitive bubbly magma shapes at the Forest Service road cut? You could salute the persons who wanted a road there and used a bulldozer to form the road surface and made what is called a road cut. The nicely shaped bubbly magma pillows and some with a magma pillow case were exposed by road construction very close the where the westward flow of magma terminated. A mile or so on the road in either direction there are other road cuts that expose basalt that is roundish, but not near as good as the EarthCache location.
These “pillow” are not for sleeping, but give you the opportunity to see a neat and not often seen geological formation. Look around and see what other neat geological features there are in Huerfano County. Within Huerfano County there are many sills that may have developed pseudo pillow lava. Million of years of weathering and erosion may have removed any exposed pseudo pillow lava, and/or vegetation covered it. I have traveled most all of the county and forest service roads in Huerfano County that are close to or cross dikes and sills and did not see what you are looking at on FS Road 415. It’s a pleasure to visit and live in Huerfano County.
Please answer the following question and email them to me. 1 What process produced the basalt pillow case(s)? 2 There is light colored soil on top of and adjacent to both sides of the basalt sill. What are your thoughts from what or where the soil came from and what process brought the soil to this area and nearby? 3 Why do the “pillow case” layers flake off the bubbly pseudo pillow basalt?
(No hints available.)