Stop 1
Miocene Quartz
Diorite Unit
Stop 1 is just
northwest of Avalon.
Stop 1 Overlook, Middle Cenozoic
(Miocene) Quartz Diorite Unit
On a clear
day this provides a great view of the continental borderland, including the
Palos Verdes Peninsula. We have been traveling through the quartz diorite unit
from Avalon. This is an intrusive igneous rock that was emplaced in the
Miocene, which was a time of marked intrusive and extrusive activity because of
crustal thinning in the continental borderland. It is intrusive but was
emplaced at shallow depth (<2 km, hypabyssal), which makes it fine grained and occasionally
porphyritic. It was highly fractured when it was uplifted and exposed on the
island. The uplift is related to the development of the proto San Andreas fault
system both in timing and mechanism, as described in the Geology section.
Quartz Diorite unit, notice the
heavy fracturing.
Video
of Humpback whales in schools of dolphin and yellowfin tuna, on the shuttle
from Dana Point to Avalon. Theres a dolphin stampede at
the end! This was October 2023.