Week 6 – Jacob Fisher – Santa Catalina Island

This week I went to Santa Catalina Island to explore its complex and interesting geology. Santa Catalina Island is one of the channel islands of the California archipelago.

Avalon, Santa Catalina Island [PHOTO: https://www.catalinaconservancy.org/index.php?s=news&p=article_55]

Geologic Map of Santa Catalina Island [PHOTO: https://maps.conservation.ca.gov/cgs/gmc/]

The island looks like an interesting mix of Cretaceous and Jurassic sandstone, Tertiary volcanic rocks with minor pyroclastic deposits, a great variety of pre-Cenozoic metasedimentary and metavolcanic rocks with small pockets of ultramafic rocks (mostly serpentine), and one small section of Miocene marine sandstone on the south eastern tip of the island.

To learn more about the island’s geology I would request:

1.     The rock that makes up Catalina Island appears to be very young but also varied. What processes occurred to create the island?

2.     This partially ties in with my first request, how does this small island have such a varied makeup? On the eastern end of the island, it is primarily Precambrian granite, on the western end it is primarily Mesozoic sandstone and portions of the middle are Tertiary volcanic rocks.

3.      Is there evidence of the island being created or partially created as part of a fold? It seems odd to me that the “KJf” rock (KJf = Cretaceous and Jurassic sandstone of the Franciscan Complex) is both on the western side and eastern side of the island.

References

Geologic Map of California (2010). (2010). Retrieved from https://maps.conservation.ca.gov/cgs/gmc/