The Nine Sisters or the Morros are a chain of twenty-three, although typically only nine are included, volcanic mountains and hills in western San Luis Obispo County, Southern California.

The peaks were created more than 20 million years ago during the Miocene Epoch of the Neogene Period, as volcanic plugs of magma which welled up and solidified inside softer rock which has since eroded away.

The peaks in order from Morro Bay to San Luis Obispo, including their height, a sortable table.

About 20 to 25 million years ago, magma welled up underneath a layer of softer rock and solidified.

[2] The Nine Sisters, being less accessible to human intrusions, support a wide variety of Coastal sage scrub and California oak woodlands flora, and of birds and other fauna.