As I soon learned, the geology of coastal California is dizzying in its complexity, because much of it is the result of the North American tectonic plate overriding the Farralon and Pacific plates over eons of geologic time, thereby “scraping” up sea-bottom sediments along with the eruption of fresh volcanic rock among everything else, then extensive faulting and folding. The older rocks along most of California’s coast are called the Franciscan Formation, a jumble of igneous and metamorphic rock, difficult to interpret in many cases. Near the coast at Jalama, what is found above the Franciscan is known as the Jalama Formation, and it is much younger, some of it as young as the Miocene. These sandstones were the rocks I saw exposed in railroad cuts.
I carefully read the book about California geology by John McPhee (one of my favorite authors), which is titled Assembling California (1994) and decided I did not really need to understand all the intricate sequences of deposition and deformation, but could simply copy the rocks I had collected. They are what are called “hand samples,” meaning they fit easily in your hand. Here is a photo of two of them, showing both the basic cream color of this formation, along with the orange-brown streaking in many layers. My dad was trained as a geologist, and no doubt he would describe these by saying “looks like country rock to me.”
[Incidentally, for those interested, all of John McPhee’s series on the geology of the United States, from the Atlantic coast to the Pacific, approximately along the fortieth parallel, is available in trade paperback, most still available new, all available used at reasonable prices. Here are the titles, shown in geographical order from east to west, though not in chronological order of publication (two were finalists for the Pulitzer Prize in Non-Fiction).
In Suspect Terrain, 1983, Farrar, Strauss & Giroux, New York (New Jersey and Appalachians)
Rising from the Plains, 1986 (describes the Rocky Mountains)
Basin and Range, 1981 (describes the Great Basin from Utah to the Sierra Nevada)
Assembling California, 1993 (Sierra Nevada to the Pacific)
There is a final title too: Annals of the Former World (1999) which collects these four volumes into one and adds the missing section from the Appalachians to the Rockies. It won the 1999 Pulitzer Prize for Non-fiction, and one reviewer wrote that it “is our finest popular survey of geology and a masterpiece of modern nonfiction.” Those wishing only to read about their area of interest can choose the relevant volume, while others may like to have all five segments under one cover.]
When I made my seaside cliff just east of the town of Jalama, I intended to have a rock cut with this distinctive local sandstone appearance. I used rubber rock molds, and first poured plaster into them and let it begin to set. Then I could apply the mold with its stiffening plaster to the contour of the underlying hillside. The mold could then complete setting shaped to the hill. I have seen modelers struggle when starting with pre-cast rocks and somehow try to fit them to a cliff or hillside. But with the “setting plaster” method, they naturally conform to what is underneath them. I didn’t invent this idea, I learned it from master scenery modeler C.J. Riley.
Once the plaster had set and molds were removed. a little paper mache was applied around the edges to blend with the hillside, and then I carefully colored the plaster rock, even inclining the strata as I had seen at Jalama. Here is a view of that rock face.
The SP section house at right completes the scene.
Unfortunately, relocating the layout locale 50 miles north means that this scene no longer represents the correct geology; but I was so pleased with the result I obtained, and the overall look of the scene I had been aiming for, that I have left it as it is. I just think of it as a small warp in space at that end of the layout.
Tony Thompson
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