Morro Rock A Volcanic Plug

This is one of the most serene, tranquil, wonderful spot on the Central California Coastline. Join Lou and Tammy to experience Morro Rock a volcanic plug and a great look at Cayucos Bay.

Morro Rock is an idyllic backdrop for Morro Bay, it is the last of the (Nine Sisters) extinct volcanic peaks along Highway 1 from San Luis Obispo.

The 581-foot (177 m) Morro Rock is one of 13 volcanic plugs (remnant necks of extinct volcanoes), lava domes, and sheetlike intrusions between Morro Bay on the north and Islay Hill on the south, all in San Luis Obispo County.

It is composed mostly of dacite, an igneous, volcanic rock, and partially of petrified bird feces, which have compacted into the plug over the years. It is a groundmass of plagioclase, with amphibole (hornblende), biotite, pyroxene (augite), quartz, and glass; phenocrysts of plagioclase, amphibole and often quartz. Its silica (SiO2) content can range from 63 to 69 percent.