A discovery that "rocks" me off my feet and even involves my favorite color, red.
The Jesusita Trail
Length: 6.8 miles For: moderate level of experience Rating: 4.5/5 stars; the waterfall brings everything together
Springtime is the best time to hike, especially when the hike ends with a flowing river that has big oak trees and sycamores filling the area and colorful wildflowers taking over. My goal became simple, I had to see all that Santa Barbara had to offer and I complied a list of all the trails that would allow me to do so. The Jesusita Trail was next on my list, being that it take more perseverance than a beginner level hike. I needed a bit more of a challenge, I felt as if my hiking skills were getting rusty. The trail was easy to follow and offered sights to numerous different landscapes, from the open and lush green grassland to the coppery tones across a plethora of rock types. As I trekked along, I couldn't help but notice the odd reddish tints that were along some outcrops.
There was no trace of this coppery red during my previous hike. Nor had I ever seen anything quite like it in Santa Barbara. I felt my friend curiosity start to join me on this hike and I knew exactly what had to be done once I arrived home. I had to dig into what was going on.
This is where the next beautiful geological piece of history begins.
The Sespe Formation
The Sespe Formation is predominantly a sedimentary rock unit that runs along the southern and south central California and specifically within the Santa Ynez Mountains. The Vaqueros and Monterey Formations lays on top on it while the Coldwater Formation [remember Cold Spring Trail?] lays beneath it. The thickness varies from 0 to 7500 feet but averages roughly 3000 feet. It was named in 1897 after the Sespe creek that flows in Ventura County. Interestingly enough and because of its vast nature, the Sespe Formation is divided into three diffferent distinctive subunits (upper, middle, lower) that have specific rock types within them.
I can't help but wonder which part of the formation that we saw at the Jesusita trail? There is also no mention of that strange red hue that paints the formation, but I know I probably need to do more digging to figure this out.
Rock(s) Description(s) (main sedimentary in nature including types of: sandstone conglomerate, mudstone, some occasional shale but has some flavor like VOLCANIC)
Since, the Sespe Formation is divided into different subgroups, the rock description must be divided as well. Using the division could aid in us deciding exactly which part of the formation we encountered on the hike. This is exactly how we will roll out.
Lower Unit
The lower unit is filled with mainly conglomerate sedimentary rocks. These conglomerates tend to be poorly sorted, meaning that they can range from numerous sizes of rocks thrown together. The main distinguishing factor of the lower unit is that some of the pieces within the conglomerate rocks are actually granitic and volcanic rocks. Granitic is a type of igneous rock (remember the three different rock types are sedimentary, igenous and metamorphic, if not, make sure to check out that geology 101 type for a refresher!) that gets its claim for fame normally by being used as table tops in fancy houses. On the other hand, the volcanic rock would have been formed from magma that erupted from a volcano.
This is something entirely mind-blowing since my little hike has now exposed me to volcanic rocks. If you want touch pieces of rock formed by a volcano, you don't even have to go to Hawaii. All you have to do is take a hike in Santa Barbara, how about that for a discovery! Of Quartz, this only intensified my love for geology!
Middle Unit
The middle unit is also filled with conglomerates and sandstones. The main difference is that the smaller pieces found within the conglomerates are actually chert and sandstones from the Franciscan complex (another formation). Chert is a type of sedimentary rock that is actually from biological origin, meaning that the creation of chert is usually from remains of different algae found in the deep ocean floor. This is another new geological encounter that we have yet experienced and only further fuels that curiosity that pulls me to dig deeper.
Upper Unit
The upper unit of the Sespe Formation is only a mix of interbedded sandstone, mudstone and siltstones. The distinctive nature of this unit is that there are no more conglomerates. This is a sharp contrast in comparison to the previous units being that both are dominated by conglomerates. There has to be an explanation for this as well, I am determined to come up with it, even if it is tuff.
Depositional Environment
The Sespe Formation creation started during the Oligocene epoch, which is roughly between 33.9 million to 23 million years before the present time. Yet, the story does not exactly start in Santa Barbara, but in San Diego, CA. The volcanic and granitic mountain ranges in San Diego are where many of the sedimentary rocks found in the Sespe Formation were created. Since this blog post is primary about the rock types found in the formation, I will leave out again the processes (plate tectonics) that allowed for the location of the Sespe Formation for another posting.
Yet, this is something that I would have never guessed while taking that hike. Not only was I seeing volcanic rocks, I was seeing volcanic rocks from San Diego!
The erosion of the San Diego mountains caused for gradual deposition of pieces of clay, silt, sand and gravel into the floodplain that would turn into the sedimentary rocks that are seen in the present day formation. This depositional environment is called continental, where deposition is either on land or in fresh water. Over time, the surface land started to change in elevation while simultaneously the sea level was increasing which caused a change in the depositional environment. It started to form a more shallower and warmer marine environment, which is similar to the Coldwater Formation from our previous hike. The sediments would now be mixed together with fossils. This was unexpected because that the fossils are not as visually obvious as they were with the Coldwater Formation.
It just goes to show that Earth is dynamically diverse in many different fields and further sparks my love for geology. After all, doesn't understanding the reasoning for Earth's beauty make it seem that much more alluring? It just further adds to the appreciation that I hold while standing at the very top of the peak, with the wind blowing through my hair as I'm holding my breath and trying to take in the glorious view of Santa Barbara.
An odd aspect of the Sespe Formation with its depositional environment is that there is a lack of information for an 8 million year time span within most of the early Oligocene. This is because of the appearance of an unconformity that is distributed through-out much of the formation. An unconformity is where during deposition stopped, then the surface proceeded to experience uplift, erosion or caving in and then deposition began again.
Geologists are currently unable to determine what exactly was happening during this period to cause this unconformity. This piece of history is a layer that is still being tackled and can offer so many opportunities for present research today. This trail possibly just opened a doorway to something that I can inquiry here during my undergrad at UCSB.
Trekking Forward
As I move forward, the dynamic geological history that fills Santa Barbara nearly knocked me off of my feet. There are still pieces unknown, more formations to learn about and even more knowledge to discover. With my geology-covered lenses, my curiosity and my hiking boots, I am capable of reaching the heights that our city offers.
The Next Hike
San Ynez Valley ft The Juncal Formation
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