The sandstone is evidence of a desert or beach environment.
The clam holes in the sandstone (see earlier page) were made below sea level.
The shale could have been formed from a tidal mudflat area.
The Principal of Original Horizontality would indicate that
these sedimentary layers were rotated to their present vertical alignment.
Although the sea level has been rising since the last glacial maximum (18,000 yr ago),
Tectonic Uplift has been greater, resulting in numerous benches or marine terraces.
The terraces number from 5 in Mendocino County's park as old as 500,000 yr
to 13 on the Palos Verdes Peninsula in Los Angeles, oldest being 2my.
The alluvium was laid down after this 1st "100,000 year old" terrace was formed.
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Sandstone base of the |
Shale vertically between sandstone |
Alluvium |
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The reddish,hard rock is jasper chert. Chert is a sedimentary rock formed from the settling of the silica rich shells of tiny marine organisms. Cinnabar is the ore from which dangerous mercury is mined. I really couldn't see the crystals! Chlorite is a green metamorphic rock or mineral formed from basalt.
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Jasper |
Cinnabar crystals |
Chlorite |
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For quartz to form, like any other mineral... requires a crack or space,fluid environment,time for the crystalization. Climb up to the trail and follow it northward. You'll notice two quartzite outcrops. Walk till they line up. Then head 50 feet to the cliff edge to find the mortar holes. Chumash or Salinan Indians? Look south and inland to see a roadcut in Cayucos and serpentine. California's state rock! Slippery when wet.
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Quartz vein |
Quartz detail |
Mortar Holes |
More Notes
You may have to hop over a small creek (San Geronimo?).Check for low tides (otherwise take the bluffs walk!).
After the mortar holes, take the path to the headland.
At low tide you can find one of California's largest populations of
Harbor Seals (some 480 total?) getting some sun on the rocks.
Click Here to return to Estero Bay 1.7