The Mid-Peninsula Region Open Space District holds an earthquake hike on the first Sunday of every month at the Los Trancos Open Space Preserve. Attending one of these and reviewing it is mandatory for all future MROSD Docents so on June 3, 2018, all but one person on this hike was a docent, future docent or spouse. The leader was John Seyfarth and Strether Smith was the sweep.
https://www.openspace.org/activities/docent/earthquake-hike-25
Because almost all of the audience was future docents, a lot of attention was placed on how to lead a nature hike.
Monte Bello has an interesting history because "The Land" commune was setup near the fault along Canyon Trail and MROSD kicked them off at 6am one morning without warning and removed all their structures. Since we were exploring the fault, we also looked for remnant of their structures. For more on this commune and their 2008 reunion, http://theland.wikispaces.org . Lone Oak Hill was used for the commune's celebrations and parties and also the Mid-Peninsula Open Space Logo.
Discuss hazards on this hike.
a. Not flat and about 2 miles plus it was in the 90's on a sunny day. Participants need basic conditioning and proper clothes.
b. Lots of ticks and we found a blade of grass with two deer ticks to show everyone.
c. Snakes. In particular, a large rattlesnake living in the culvert under the trail to "rattlesnake viewpoint." It wasn't out but we went looking for it.
d. Poison Oak and lots of it.
Expectations:
a. This is a nature, education hike and won't be going very fast or far.
b. It's hot and dry.
c. Survey the participants by making them raise 1-5 fingers based on expertise. One professional geologist and one whose undergraduate degree in geophysics.
Additional Resources. Strether showed three books (some of which are out of print and now expensive.) "Field Guide to the San Andreas Fault," "Geology of the SF Bay Area," and "The South Skyline Story."
http://thulescientific.com/Front.htm
https://www.ucpress.edu/book/9780520241268/geology-of-the-san-francisco-bay-region
http://southskyline.org/history-2/
We walked up to "rattlesnake point" after crossing the culvert and admired the many wildflowers still blooming. At rattlesnake point, Strether pointed out the conglomerate rocks which were from Loma Prieta Peak, 23 miles to the South on the North American Plate. We were on the North moving Pacific plate. https://www.inaturalist.org/observations/13104738
https://www.inaturalist.org/observations/13104737
https://www.inaturalist.org/observations/13104736
https://www.inaturalist.org/observations/13104735
https://www.inaturalist.org/observations/13104734
https://www.inaturalist.org/observations/13104732
Also from this point we could see Black Mountain which is either the largest or the third largest piece of Limestone known. Cinnabar Winery built huge caves in the limestone to store it's wine. Ridge Winery is also just past Black Mountain.
Black Mountain itself is still growing because of an S Curve in the San Andreas Fault. Strether took out a Raisin Bran Cereal box back with an S Curve and showed how the north moving Pacific Plate was compressing the area south of Black Mountain and forcing it up.
I've taken this view so many times that I didn't take it this day. However, you can see both the San Andreas and the Pilarcitos Fault zones. The Pilarcitos Fault runs along the Stevens Creek headwaters to Half Moon Bay and it used to mark the boundary of the Pacific and North American Plates but for some reason that boundary moved inland to the San Andreas Fault which follows Canyon Trail through Portola Valley and Woodside to Crystal Springs Reservoir now. https://pubs.usgs.gov/of/2005/1127/chapter8.pdf
We stopped along the trail toward Canyon Trail to look for fossils in the pebbles didn't find any and we examined the remnants of past human settlements. The black walnut grove was planted by a homesteader who gave up after the 1906 earthquake.
https://www.inaturalist.org/observations/13104739
https://www.inaturalist.org/observations/13104729
While walking along the the Canyon Trail, we saw tar weed, salsify and gold back ferns and lots of grasses.
https://www.inaturalist.org/observations/13104725
https://www.inaturalist.org/observations/13104742
After crossing Page Mill Rd back to the Los Trancos Earthquake Trail, we found some wild strawberries.
https://www.inaturalist.org/observations/13104824
And we talked about why one particular trail was now closed due to infestation of Sudden Oak Death in the trees around it. Much of the discussion came from Frances, the retired Ranger, who knew about early spraying efforts to stop the spread of Sudden Oak Death and the futility of trying to clean off our shoes to prevent its spread. Sudden Oak Death is caused by an old world phthiraptera water mold and is spread by the wind during foggy days. It affects more than just oaks and it's likely it can't be stopped.
http://www.suddenoakdeath.org/about-sudden-oak-death/faq/
15, At a wide trail junction, Strether used a slinky attached to a board with a rattle to demonstrate P- and S-waves and their speed and damage they cause. By dragging the board on the trail, he demonstrated the stickiness and unpredictability of sliding motion.
Finally we talked about dating the 1906 quake from new growth from fallen trees. A tree topples over but doesn't die and new branches grow vertically out of the fallen trunk.
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