The Rock at Morro Bay
Photo © Debbie
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.
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
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
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