What's in a Sand Dune?

I was traveling up Highway 1 the other day. I was past County Line and less than a mile north of Sycamore Canyon, in full view of Point Mugu, when I spotted what I had been hearing about—the very steep, long sand dune at Thornhill Broome. It was like finding an archaeological treasure ... more like a geological treasure. 

I thought I would get a daily dose of exercise by ascending this steep wall of sand ... it wasn't going to be easy. I put one bare foot in front of the other and watched as the sand crumbled down the slope with each step. I made it to the top and looked back at the ocean. The ocean never appeared more vast and overwhelming than that day. I was at a vista that was virtually unchanged since the days of the Chumash. When Juan Rodriguez Cabrillo, in 1542, landed not too far from here, the vista was as I saw it that day … no boats, no signage or stamp of man, save for the slender Pacific Coast Highway. 

As I came back down, and then up again, I couldn't let go of the thought that all of this sand was being driven down the slope and toward the highway below. While I was there, I didn't see any sand travel back up the slope, nary a single grain. Over time, I thought, with countless trekkers up and down this steep sand dune, with relentless gravity, surely the sand should all be at the bottom of the slope by now. There was no place above from where the sand could have originated.  If gravity, and all the forces generated by man via walking up and down this dune brought the sand down the slope, then what forces could be maintaining the homeostasis of the dune, such that it looks virtually the same now that it did when John C. Fremont and Pio Pico signed the treaty of Guadalupe Hidalgo in 1848, making California the permanent sovereignty of the United States and ending the US/Mexico War? 

Could there be a force that compensates for the downward forces? And if so, how could that "force" balance perfectly those downward forces? The answer, however obvious, is one of the most powerful forces in all of nature, the force that causes wave formation and tornado formation and hurricanes. The force that women (and some men) hate after they have just left the hair salon. Yes, the wind is responsible for transporting that sand back up the slope. The strong, and consistent onshore winds from the Pacific Ocean are prominent enough to keep that sand comfortably up that slope … the Thornhill Broome. 

What causes those onshore winds? The cold air from the ocean travels onto land as a result of the vacuum created when hot air over the land rises. Onshore winds are about 10 times more common than offshore winds.  The Santa Ana winds, which are the result of a high-pressure system on land, are responsible for the most powerful of offshore forces, however, they aren't nearly enough to compensate for insidious and predictable onshore forces.

When the wind moves particles (sand in this case) over land it is called Aeolian transport. There is no question that this sand came from the beach below, on the other side of PCH. How much the construction of the PCH in this area (sometime in the 1920s) affects that sand dune I could only guess. The wind is just an awesome force in nature, from my vantage point at the top of the dune one could have no doubt witnessed some Apocalyptic displays of such wind. 

I urge you to make a trip there, if only to look up and marvel. If you do venture up the slope, please replace the sand that your feet have displaced down the slope lest all of the sand will eventually end up at the bottom (just checking to see if you have been paying attention).   Hope to see you there ...  If you are lucky you might see the topgallants of Rodriguez's sea vessel coming south around Point Mugu. It's pure sanctuary!