Morro Dunes form a barrier spit that separates Morro Bay to the east from the Pacific Ocean to the west, about 6 miles (10 km) south-southwest of the community of Morro Bay and 2 miles (3.2 km) west of Los Osos, California. The dunes are named after the bay, which in turn was named for the prominent rock at its entrance. ‘Morro’ is a Spanish geographical term for a crown-shaped rock or hill. The northern end of the spit is designated as the Morro Dunes Natural Preserve, a northern extension of Montaña de Oro State Park. ‘Montaña de Oro’ means ‘mountain of gold’ in Spanish, a reference to the golden wildflowers that bloom in the area. Coastal dunes form landward of the beach where prevailing onshore winds and a consistent supply of sand allow for accumulation. Wind speed, direction, and sand grain size influence the size and shape of dune systems. Sand is deposited when wind carrying it encounters an obstacle—such as driftwood, seaweed, or trash—which reduces wind velocity. More often, salt-tolerant vegetation like grasses, shrubs, or trees serves as the main obstacle, promoting sand deposition and stabilizing the dunes. Under fair-weather conditions, the base of dunes is typically unaffected by wave energy. However, during storms and elevated sea levels, breaking waves may erode dunes, causing blowouts or overwash. Eroded sediment can be carried inland and deposited in adjacent estuaries, forming tidal flats. Well-established dunes act as natural barriers, shielding inland infrastructure from storm surge. As such, dune systems are often protected to mitigate erosion and preserve stabilizing vegetation.

When Europeans arrived in Alta California in the 1500s, the Chumash lived in small coastal villages between Morro Bay and Malibu. The closest known settlement to Morro Bay is the Back Bay archaeological site in Los Osos, situated on a stabilized dune and dating from AD 800 to 1200. In 1769, Don Gaspar de Portola led an expedition north from San Diego, initiating the California Mission period. Coastal Indigenous communities were relocated to missions, where many died from European diseases. Following Mexican independence in 1821, mission lands were secularized. In 1842, Governor Juan B. Alvarado granted Rancho Cañada de los Osos (‘valley of the bears’) to Victor Linares, a former majordomo and militia commander at Mission San Luis Obispo. Two years later, John D. Wilson and James G. Scott purchased Rancho Cañada de los Osos and the adjoining Rancho Pecho y Islay to the south, originally granted in 1843 to Francisco Badillo. In 1845, the ranchos were combined into Rancho Cañada de los Osos y Pecho y Islay, covering 32,431 acres (13,124 ha) and 7 miles (11 km) of Pacific coastline between Morro Bay and Islay Creek. During the Bear Flag Revolt in 1846, American settlers challenged Mexican rule, leading to the Mexican-American War. The 1848 Treaty of Guadalupe Hidalgo ended the conflict, and California became a US state in 1850. In 1861, the rancho passed to Wilson’s wife, Maria Ramona Carrillo Wilson, and their daughter Ramona Hilliard, who used it for sheep grazing. Portions were later sold or leased for ranching and dairy operations. In 1963, half the Pecho ranch became Montaña de Oro State Park; the remainder is owned by Pacific Gas and Electric. The Morro Dunes area was annexed to the park to protect endangered species, including the western snowy plover and Morro blue butterfly.

Morro Bay is a 2,300-acre (931 ha) estuary fed by Chorro and Los Osos Creeks, which drain a combined watershed of 48,000 acres (19,425 ha). The bay is part of the National Estuary Program and includes a state park, a state marine reserve, and a state marine recreational management area. Established in 1987 through amendments to the Clean Water Act, the National Estuary Program aims to protect and restore estuaries of national significance. It addresses water quality alongside the ecological, economic, and recreational integrity of entire estuarine systems. Morro Bay State Park comprises two areas: one borders a lagoon at the mouth of Chorro Creek, featuring saltwater and brackish marshes that support abundant birdlife; the other includes the coastal dunes on the sand spit, now part of Morro Dunes Natural Preserve. The Morro Bay State Marine Reserve lies at the confluence of Chorro and Los Osos Creeks and protects all marine life within its boundaries. Fishing and the taking of any living marine resources are prohibited below mean high tide. Adjacent to the reserve, the Morro Bay State Marine Recreational Management Area protects marine life near the bay entrance and west of the reserve. In about the southern third of the bay, taking marine life is also prohibited. In the northern two-thirds, recreational finfish harvest and oyster aquaculture are conditionally permitted. Key environmental concerns for the Morro Bay National Estuary include accelerated sedimentation, bacterial contamination, excess nutrients, toxic pollutants, reduced freshwater inflow, biodiversity loss, and the challenge of balancing environmental protection with human use. Read more here and here. Explore more of the Morro Dunes and Los Osos here: