I talked to Rich yesterday & further emailed him today to clarify some of what he's said about scrub oak and the surrounding area. For self-reference clarification: Chaparral is an umbrella term for evergreen shrubs, such as scrub oak. Coastal sage scrub are also shrubs, but they are drought deciduous. The 13,000 year old Palmer oak in Jurupa Hills is not actually scrub oak. We talked about different distributions of scrub oak throughout southern California and throughout the Baja as well, in both past and present times in order to give context to the late Pleistocene climate. In relation to the project, we have a fossil of a scrub oak found in an area where only coastal sage scrub grows now. Climate change and a shift in vegetation are important facets to consider throughout this project.
He showed me an aerial shot of Joshua Tree National Park and how there were some flourishing tree populations at the bases of the large, fractured rocks found there. While there is little rainfall, it all collects on the rocks and runs off to the base, where these plants flourish. Likewise, rainfall can be absorbed by the rocks and precipitated out. This is directly relevant to the Box Springs area, where, true to the name, there are a couple streams emanating from the granitic bedrock. He showed me the aerial shots of these two stream areas and how there are sycamore and willows growing there, two of the specimens found in the fossils. He also showed me the only two (perhaps three) scrub oak known to be in the entire area, also near these stream areas, seeing as all three of these are stream plants and require plenty of water to flourish.
In direct correlation to the project, it got me thinking specifically about how the fossils came to rest there. The original assumption was that they were growing there, especially since the place in which the road is now happens to be a stream bed for water (as it is lower than the surrounding areas). However, Rich mentioned something that caught my attention. He mentioned that maybe the Sycamore leaf could've blown in from far away and become fossilized with the others despite not having been present in that location - but because they are all stream plants that can coexist in the same type of environment, it seems to me that they are all most likely from the same location and that they could not have all blown in on their own.
This lead me to think of something else: as I mentioned, the original assumption was that they were growing there together. However, seeing as they were fossilized all at the same time in an instant burial event, I still find it strange that we could not find any other indication of sandstone in the area. This would seem to imply, at least to me, that it's plausible these plants were actually washed into the lower area by the stream of water during the flooding event. If there was a dip in the ground, the water could have brought the leaves from further upstream and dumped them into a puddle all together, where they mixed with the sediment and became fossilized. Their proximity to each other may not actually be indicative of dense foliage in that specific area during LGM conditions, but actually of denser scrub oak and willow/sycamore communities at a slightly higher elevation in the Box Springs hills (which would still be consistent with what we know, but could indicate the fossils are from later in the Pleistocene or early Holocene). If sandstone only formed in small pockets in the Box Springs hills where the sediment deposition rates are higher, it would coincide with the fact that most of the geology of the area is granitic without enough topsoil or proper conditions to form sandstone atop the granite.
The sandstone containing the fossils is also very fine. Outside of the flooding event, it means that location in particular had to be very low energy. The other piece of sandstone we found higher up in the hills is less fine, and gives the impression that it's an unrelated piece of sandstone - if it is indeed from Box Springs, it's possible that multiple pockets of sandstone were formed in different locations, possibly some not now covered by the road. I'm curious if it would be possible to find any of these places and find more clues as to how these pockets of sedimentary rock were able to form.
I feel it's important not only to put the climatic context of these fossils into place, but to also consider all methods and possibilities of how they came to rest there and what processes had to take place in order to ensure their fossilization. As I continue to do more literary research into Pleistocene climate and the plant content of ancient pack rat middens, I will also be attempting to put my knowledge of the geology of Box Springs to think of all the possible pieces to the puzzle we can put together.