major streams rising from the western side of the range drain into the Pacific Ocean; these include Peters Canyon Wash, Serrano Creek, San Diego Creek, Aliso Creek, Trabuco Creek, San Juan Creek, and San Mateo Creek. The northern side of the range is defined by the Santa Ana River, which heads about further east, in the San Bernardino Mountains. Santiago Creek drains much of the northern part of the range and empties into the Santa Ana River near downtown Orange. Water from the north-east side of the range empties into Temescal Creek which flows north to the Santa Ana River, or Lake Elsinore which intermittently overflows to Temescal Creek. The southeast end of the range is marked by the Santa Margarita River, which also originates east of the Santa Anas and flows southwest to the Pacific. Runoff from the southeast side of the range drains into Murrieta Creek, a tributary of the Santa Margarita River. Irvine Lake, the largest body of fresh water in Orange County, is in the northwest part of the range near Villa Park. The lake is formed by the Santiago Dam, which impounds Santiago Creek. Climate The climate is Mediterranean, with warm dry summers and cool wet winters. Annual precipitation totals range from 20 to 30 inches (500–760 mm) in the higher parts of the range above 3,000 feet (910m), as compared to the average of 13–16 inches (350–400 mm) in the coastal plain. Most of the precipitation falls between November and March. The western (coastal) slope is generally moister than the eastern slope. Snow falls during winter on the highest peaks. Human history The mountains were named by members of Gaspar de Portolà's expedition, who camped below the mountains on July 26, 1769, the Feast Day of Saint Anne. At the time of Portola's visit, the Santa Anas were settled by three main groups of indigenous peoples, the Tongva in the north, the Acjachemen in the west and Payomkowishum in the east and south. A handful of historic sites remain in the range today. Registered California Historical Landmarks include an Indian Village Site in Black Star Canyon, Flores Peak named for the outlaw Juan Flores, the mining boomtown sites of Carbondale and Silverado, and Helena Modjeska's home. The Moreno and Machado Adobes of the Rancho Santa Rosa are found on the Santa Rosa Plateau Ecological Reserve. Beeks Place, a small house foundation still owned by