San Miguel Island is the westernmost of California's Channel Islands, located across the Santa Barbara Channel in the Pacific Ocean, within Santa Barbara County, California. San Miguel is the sixth-largest of the eight Channel Islands at 9,325 acres (37.74 km² or 14.57 sq mi), including offshore islands and rocks. Prince Island, 700 m (2,300 ft) off the northeastern coast, measures 35 acres (14 ha) in area. The island, at its farthest extent, is 8 miles (13 km) long and 3.7 miles (6.0 km) wide.
San Miguel Island is part of Channel Islands National Park, and almost all of the island (8,960 acres (36.3 km2)) has also been designated as an archaeological district on the National Register of Historic Places. This westernmost Channel Island receives northwesterly winds and severe weather from the open ocean. The cold and nutrient-rich water surrounding the island is home to a diverse array of sea life that is not found on the southern islands.
San Miguel Island, together with numerous small islets around it, is defined by the United States Census Bureau as Block 3010, Block Group 3, Census Tract 29.10 of Santa Barbara County, California. The island is uninhabited. Highest peak is San Miguel Hill, at 831 feet (253 m). Submerged rocks make the nearly 28-mile (45 km) coastline a mariner's nightmare.