The Carrizo Plain is a large enclosed grassland plain, approximately 50 miles (80 km) long and up to 15 miles (24 km) across, in southeastern San Luis Obispo County, California, about 100 miles (160 km) northwest of Los Angeles. It contains the 246,812-acre (99,881 ha) Carrizo Plain National Monument, and it is the largest single native grassland remaining in California. It includes Painted Rock in the Carrizo Plain Rock Art Discontiguous District, which is listed on the National Register of Historic Places. In 2012 it was further designated a National Historic Landmark due to its archeological value. The San Andreas Fault cuts across the plain.

The plain extends northwest from the town of Maricopa, following the San Andreas Fault. Bordering the plain to the northeast is the Temblor Range, on the other side of which is the California Central Valley. Bordering the plain to the southwest is the Caliente Range. The community of California Valley is on the northern part of the plain. The average elevation of the plain is about 2,200 ft (700 m). Soda Lake, a 3,000-acre (12 km2) alkaline lake, is in the center of the plain with the popular Painted Rock containing Chumash and Yokut rock art nearby. As the central depression in an enclosed basin, Soda Lake receives all of the runoff from both sides of the plain. At 5,106 ft (1,556 m), Caliente Mountain, southwest of the plain, stands as the highest point in San Luis Obispo County. The climate type of the Carrizo Plain is semi-arid grassland. No trees grow there and the annual rainfall is around 9 inches (230 mm) per year.

The Carrizo Plain is an easily accessible place to see surface fractures of the San Andreas Fault; they are clearly visible along the eastern side of the plain, at the foot of the Temblor Range. They are best seen in early morning and evening light, when shadows enhance the topography. In addition to its spring wildflower displays, Carrizo Plain is famous for Painted Rock, a sandstone alcove adorned with pictographs created by the Chumash people around 2000 BC.

State Route 166 passes the south entrance to the Carrizo Plain, and State Route 58 crosses through the northern portion. Connecting them is the narrow Soda Lake Road, the only dependably passable road through the plain—but even this may become impassable during or soon after a rain since the middle portion of it is gravel.

The most prevalent geologic feature of the Carrizo plain is the San Andreas Fault, a right lateral strike-slip fault which runs along the northeast side of the plain, at the base of the Elkhorn Scarp. The San Andreas fault forms the boundary between the Pacific and North American plates, extending ~850 miles (1370 km) along the western coast of California from Cape Mendocino in the north to just south of the Salton Sea near the US-Mexico border. The section of the fault in the Carrizo plain is the oldest section along the entire fault zone, where cumulative right-lateral offset is ~195 miles (~315 km) since early Miocene time. Displacement on the San Andreas is responsible for the development of distinctive geomorphic features along the fault trace, including shutter ridges, diverted and/or decapitated stream channels, and sag ponds.

en.wikipedia.org/wiki/Carrizo_Plain