Los Trancos is one of the Open Space preserves, the previous ones that w
e visited were Rancho San Antonio and Syline Ridge. We had been wanting to hike along the San Andreas fault ever since "A" started her science project on "What causes earthquakes?".
e visited were Rancho San Antonio and Syline Ridge. We had been wanting to hike along the San Andreas fault ever since "A" started her science project on "What causes earthquakes?". Docent led fault hikes are scheduled every month at Los Trancos and this time we happened to be there!
San Andreas fault is 810 miles long transform fault between the North American and the Pacific plate and along the coast of California. 1906 San Francisco earth quake and the 1989 Loma Prieta earthquakes are the product of this fault. Along these 2 plates there is no single fault line, it is a wide zone having multiple faults such as the Hayward and the Calaveras.
The fault 
trail is about 3 miles loop trail and is easy hike, so kids are welcome. Along the hike are stations/posts (with yellow paint) marked 1-9 which represent the various earthquake artifacts. Also along the hike there are posts marked with white paint and these indicate where the fault line for 1906 earthquake was.
trail is about 3 miles loop trail and is easy hike, so kids are welcome. Along the hike are stations/posts (with yellow paint) marked 1-9 which represent the various earthquake artifacts. Also along the hike there are posts marked with white paint and these indicate where the fault line for 1906 earthquake was. Following is what we experienced, at each of the 9 stations,
Station 1:
This station offers a view to the Mount Umunhum and Loma Prieta. When standing at this station, you are on the Pacific plate, while the Loma Prieta is on the American plate. The docent pointed out the rocks which look as if round pebbles are ce
mented in sand. The scientists found similar rounded rocks at Loma Prieta and came up with the hypothesis that millions of years ago, a river or stream flowed from American plate on to the Pacific plate and carried the smooth rocks. Since then about 12,000 earthquakes have occured along the fault and caused the Pacific plate to move.
mented in sand. The scientists found similar rounded rocks at Loma Prieta and came up with the hypothesis that millions of years ago, a river or stream flowed from American plate on to the Pacific plate and carried the smooth rocks. Since then about 12,000 earthquakes have occured along the fault and caused the Pacific plate to move.
Station 2:
From here we could view the Crystal spring reservoir and San Andreas Lake. These are formed by the dam built right on the fault to provide water to San Francisco. Although it was not known then.Station 3:
It is the most interesting station as this is where the actual slip had occure
d and in 1906 after the earthquake, crack could be seen. The plates have moved apart here, however over the years the cracks got filled by soil and it forms what is called as a "bench".
d and in 1906 after the earthquake, crack could be seen. The plates have moved apart here, however over the years the cracks got filled by soil and it forms what is called as a "bench". Usually a valley is steep and there is smooth descent, but in a bench there is a raised portion, then an unusual flat area and then again another raise (not quiet high as the first one). We did a activity where some of us were on Pacific plate(left side) and others on the American plate(right side). The docent mentioned that the place where we stood had a small layer of top soil on bed rock, hence that place would not suffer much of a damage in case of earthquake.
Station 4:
This is where we saw another artifact, a wooden fence(which has been re-constructed since the earthquake) which shows how a slip and strike earthquake can change the alignment of any structure that goes across the fault.
Station 5:
Springs or unusual wet areas are another feature of earthquake zone and this can be seen at this station.
Station 6:
Here you could see the sag pond in spring and may be just a shallow depression with no water in summer. The sag pond is formed when the 2 plates move away from each other creating a depression that gets filled with water from rain. The sag ponds are often found in the earthquake zones.
Station 7:
Here we saw 2 unusual oak trees, which fell during the earthquake. They were still rooted and hence kept growing. The lower part of the trunk is horizontal and the rest of the tree is vertical 
Station 8:
At this station we saw the valley/depression formed either by land slide or fault movement, usually valleys are formed by flowing water.
Station 9:
At this station too we saw the bench like feature.
Along the trail the docent pointed 
out canyon oak, black oak trees, tan oak trees as well as Yerba buena herb(mint family), bay tree, red maid, hounds tongue (since the leaves are furry and have shape of a dog's tongue), poison oak etc. We also saw a tree with hollow trunk which was still alive because its cambium was still intact. The docent mentioned that in sudden oak death, the sapwood and cambium are destroyed and hence the tree dies.
out canyon oak, black oak trees, tan oak trees as well as Yerba buena herb(mint family), bay tree, red maid, hounds tongue (since the leaves are furry and have shape of a dog's tongue), poison oak etc. We also saw a tree with hollow trunk which was still alive because its cambium was still intact. The docent mentioned that in sudden oak death, the sapwood and cambium are destroyed and hence the tree dies. This trail is fun and educational and we are looking forward to go again. The only caveat is the uphill drive on winding Page Mill road.
No comments:
Post a Comment