One More From the Coast

As I mentioned in my post on Sea Lion Caves, it was pretty rainy and blustery the day we went over there (two weeks ago today). Below is the view south from the headland into which the cave is eroded.
The N/S fault that formed the major plane of weakness that allowed erosion to create the cave cuts off the stack in the midground. The coastal town of Florence lies somewhere out there in the gloom. Between Florence and the next town to the north, Yachats (pronounced yah-hahts; Oregonians get very touchy about mispronounced place names), lies a beautiful stretch of rocky headlands. These rocks, the Yachats Basalt, are younger than the Siletz River Volcanics that make up most of the Coast Range accreted terrane known as Sileztia. (More on Siletzia at the end of this post) I have never been clear about the origin and age of the Yachats Basalt, but fortunately, my focus in this post is more on the much younger stuff to the south.
The above GoogleEarth image shows fairly clearly the boundary between the basaltic headlands to the north and the dunes southward into Florence. (I have moved the scale bar to the middle of the picture.) Sea Lion Cave is about where the label "Cox Rock" is. This stretch of dunes continues south to Coos Bay, 40 to 45 miles as the crow flies. Some of the dunes rise over 500 feet high, and make for great field trip stops. From a geological perspective, dunes are pretty straightforward (i.e. simple), and for some reason I find them much more interesting when they're lithified. From an ecological and biological perspective, though, they are even more fascinating.

The above photo shows a couple of interesting features: first, there is a constant tension between colonizing plants and moving sand- the two don't play well together. Moving sand swamps and suffocates plants, while plants stabilize the sand and prevent it from moving. I imagine this as a constantly shifting patchwork of green and beige. Second, the flow of sand is fast enough that most smaller streams in this area never reach the ocean. They are impounded behind a wall of sand, then drain out to the ocean as groundwater. In the above case the two small pools have neither inflowing surface water nor outflowing surface water. I'm presuming that during drier periods these basins are excavated and eroded by strong coastal winds and local vortices. During wet periods (as during this trip), the groundwater rises above the ground's surface.

I suspect that the above lake does have an inflowing stream, but drains through the permiable sandy substrate.

Since the sand is dominantly quartz, with the remainder fresh lithic fragments, as soils go the ground is very poor in nutrients. Forest with quite large trees can become established, but only after hundreds of years of succesion, typically going through beach grasses, brushy plants like salal and Oregon grape, and finally young trees, creating and storing enough organic matter that the ground can support a mature forest.In the above picture, the leaves with a "normal" shape are salal. Since standing water prevents the oxidation and decay of organic material, nitrogen tends to be in short supply in wetlands within the dunes. The odd cobra shaped leaves are those of Darlingtonia Californica, a plant that has evolved a surprising set of charateristics to deal with this situation.
A denser patch of the plant that makes it more obvious why its common name is the Cobra Lily. While not venemous like its namesake, it is carnivorous. Unlike the well-known Venus Flytrap, pitcher plant are passive carnivores; they don't actually move to capture their prey. I had been planning to write out the various adaptations they use to do this, but Wikipedia has a photo of the sign from this wayside that explains it as well as I could. The photo linked above is from the article that discusses this small but fascinating break from geologizing along the Oregon Coast- though as I have implied here, the geology plays an important role in creating an environment where the specialized features of this plant allow it to successfully compete with other species.
The crop above is from the lower right of the previous picture, and shows the opening to the interior of one of the pitcher-shaped leaves. The upright leaf in the lower middle shows the lighter spots, or "skylights." These are translucent spots that fool flying insects into trying to fly through the "roof" of the leaf, rather than exiting from the lower opening.