Morro Rock was named in 1542 by Portuguese navigator Juan Rodriguez Cabrillo, who explored the Pacific Coast for Spain. Cabrillo called the rock El Moro because it resembled the head of a Moor, known for the turbans they wore. Cabrillo also named the bay Los Estoros. 

 

Morro Rock is one of a line of ancient volcanic intrusions or plugs sometimes called the Seven Sisters or The Nine Morros, depending on how many of the peaks are included in the count, are a unique set of landmarks between the city of Morro Bay and the City of San Luis Obispo. These ancient volcanic mountains are scenic peaks that include Morro Rock, Black Hill, Cerro Cabrillo, Hollister Peak, Cerro Romauldo, Chumash Peak, Cerro San Luis Obispo, and Islay Hill within the City of San Luis Obispo. Stunted Terrace Hill and submerged Davidson's Seamount are omitted. Forming a backdrop for the Cities of San Luis Obispo and Morro Bay and a divider between the Los Osos Valley and Chorro Valley, these peaks cover approximately 40 square miles. Aptly named the Nine Sisters because they are all in a row and in close proximity, the nine have had their names designated on the Geological Survey maps since 1964.

 

The present elevation of Morro Rock is 581 feet.  The Army Corps of Engineers on several occasion used the Rock as a quarry to provide materials to construct breakwaters and other facilities. This practice was terminated in 1969 when the State of California gained full title from the United States Congress.  Morro Rock is now listed as State Landmark #801. 

 

Evidence supports a theory that the morros erupted along old fault lines, leading to a hot spot deep within the earth. Morro Rock is dated to about 22 million years old. Black Hill, rising behind the Morro Bay Golf Course, and Hollister Peak are about 28 million years old during the Oligocene epoch of geologic history. The Morros may have formed south of the region with their remnants moving along the San Andreas fault to their current positions. 

Many other changes took place over the millions of years since Morro Rock solidified. About eighteen to twenty thousand years ago, the sea was 300 feet lower than it is today. Morro Rock stood on dry land. After the last glacial retreat, the sea rose again and Morro Rock was surrounded by salt water. A causeway to Morro Rock was made in 1933 through the Works Progress Administration. A causeway was created with materials blasted from the rock. 

The volcanic plugs tend to have steep sides of exposed rock, although buttresses slope from these peaks to make all of them accessible.  The Chorro Valley surrounds the Morros and features several hundred Chumash Indian mortar sites. If you would like to learn more about the history and geology of Morro Rock and other morros, visit the Morro Bay Museum of Natural History.