One of the unique features of Santa Barbara County is it geology. Many on the rocks we now see around us were formed underwater in the ocean and then uplifted. Santa Barbara, along with the rest of coastal California from Pt. Reyes down to the border, as well as all of Baja California are part of the Pacific tectonic plate, which is slowing inching its way northward as it slides against the North American Plate along the San Andreas Fault.
These different forces created our local mountains and in the process exposed a wide variety of rock and soils types, this is both a boon to those interested in geology, but also the reason why we are blessed with so many different types of plants. Many of our local plants are adapted to specific soil types, the more types of rocks and soils the more opportunity for adaptation.
A while back the Santa Barbara Ranger District designed a self-guided interpretive hike from Upper Oso to Nineteen Oaks and published a corresponding pamphlet entitled “Geologic Trail Guide for the Upper Oso Canyon”.
And although the interpretive trail was never completed the guide itself is still quite useful as many of the features highlighted are relatively easy to locate once you know what to look for. The guide is well written and includes a map of the hike on a Thomas Dibblee style geologic map. The map also includes where the 16 stops were intended to be and so between that and being able to spot some of the more recognizable features on the landscape one can still follow along. The hike to Nineteen Oaks is 3.5 miles round trip.
Copies of the guide are free at the Forest Service’s administrative offices in Goleta, at 6755 Hollister Avenue, Suite 150. Or click here for a PDF version of the brochure from the Forest Service website.
To get to the trailhead from Santa Barbara take State Route 154 over San Marcos Pass to Paradise Road, turn right on to Paradise Road and follow it to Lower Oso Day Use Area, just past the first crossing of the Santa Ynez River. At Lower Oso the road splits with Paradise Road continuing towards Red Rock to the right and the Camuesa Road continuing to the left towards Upper Oso.
Stay to the left and follow Camuesa Road as it makes it way through Lower Oso Canyon and arrives at Upper Oso Campground. Stay to the right and follow the road to the locked Forest Service gate at the beginning of the Buckhorn-Camuesa Road, where there is parking. An adventure pass is still required to park or camp in this part of the Los Padres National Forest.
From the trailhead, the trail follows the Buckhorn-Camuesa Road for the first .75 miles. The dirt road is open to OHV (off-highway vehicles) traffic and so you will need to be alert to motorcycles and small ATVs using the road.
The road follows Oso Creek and one of the more noticeable features on the hillsides, particularly on the left or west side of the canyon is the visible outcroppings of sandstone. As the canyon narrows both the creek and the road literally pass through this bed of Matilija Sandstone. Sandstone is a type sedimentary rock that is formed from sand that has been cemented together over time. Sandstone was used by the Chumash for their rock mortars and forms many of the caves used for their paintings. Stop #2 highlights the large Matilija Sandstone overhang on the right hand side of the road.
As the road continues it passes by another exposed outcrop of Matilija Sandstone also on the right (stop #3). Here the rock is more eroded than the previous outcropping, as the sandstone is intercut with layers of Siltstone which is made up of finer particles and is more easily eroded. If you look closely you can even see small round holes and channels in the rock where sea worms once burrowed when the rock was part of the ocean floor.
Just passed this rock feature, as the road rounds the corner, you can view on your left across the canyon a noticeable exposed rock scarp or steep, eroded slope (stop #4) and then as you continue the road passes by the same rock bed on the right side of the canyon (stop #5). This rock bed is made up of more easily eroded Matilija Siltstone.
At the .75-mile mark the trail arrives at the beginning of the Santa Cruz Trail, where the interpretative hike continues. However one can make a slight detour along the Buckhorn-Camuesa road to visit stop #6. The road double backs and then makes a hairpin turn, just after which on your left is a white carsonite sign where stop #6 would be. From this vantage one can look across the valley and view a concave fold in the bedrock known as the Oso Syncline.
The hike continues along Santa Cruz Trail as it follows Oso Creek and here again the canyon narrows passing through another bed of Matilija Sandstone, after which the canyon opens up.
The trail then transitions into much older rock uplifted by the Little Pine Fault, the fault is not easy to see, but the rocks themselves are noticeably different, even in color, transitioning from sandstone to olive and gray.
The trail then crosses the creek twice in quick succession (stop #9) where if one turns and looks back down the canyon one can see on their left a rocky ridge comprised of olive-colored Espada Formation rocks.
The next few stops in the guide highlights several different Metamorphic Rocks found in what’s know as the Franciscan Assemblage, that one can find both along the trail and down in creek. Metamorphic Rocks are sedimentary rocks that were subducted, and exposed to both high temperatures and pressure that changed their chemical structure and appearance.
The first of these metamorphic rocks that one can see along the trail is Serpentine, with its distinctive green color. A particularly good example can found where a side wash that is noticeably loaded with serpentine and other rocks crosses the trail.
More or less around the corner from this side wash, the trail passes a large rust color boulder that appears to be made of folder layers of rock. This rock, called Chert, is made from the silica skeletons of tiny marine organisms that was later folder and compressed.
The third metamorphic rock highlighted is Blueschist, which is a rare blue-grey colored rock visible down in the creek just past the red-banded chert. There is also a large blueschist boulder in the middle of the creek back at the creek crossing.
At about the 1.75-mile mark the trail arrives at the turnoff for Nineteen Oaks, from here it’s less than a quarter mile to the camp. The trail climbs away from the creek and passes a large rock outcropping on your left (stop #15). If you look closely at this rock you can see what’s referred to as slickensides. These grooves are created when a fault slips and two pieces of rock grind against one another.
Just past this rock formation the trail arrives at Nineteen Oaks. The camp itself is situated on the top of an ancient landslide that is dotted with outcroppings of Franciscan Rock. There is a trail that continues further up the canyon for additional exploring.
Nineteen Oaks can also make for a nice overnight backpacking destination. There are two campsites each with a fire ring and picnic table.
Regardless how far you go you will have a chance to see some of the geologic history of Santa Barbara County.
This article originally appeared in section A of of the July 14th, 2012 of the Santa Barbara News-Press