Santa Clarita Valley (not similar sounding Santa Clara) contains one of the larger cities in LA County, as well as many other developments. The valley was part of the Rancho San Francisco Mexican land grant. Some of the communities within it include the city of Santa Clarita, which is made up of Canyon Country, Newhall, Saugus, and Valencia. Adjacent unincorporated communities include Castaic, Stevenson Ranch, Sunset Pointe, Tesoro, Val Verde, Westridge and the new master planned community of Newhall Ranch.
Downstream of Santa Clarita, the valley is called Heritage Valley, consisting of Piru, Fillmore, and Santa Paula. The upstream portion is called Soledad Canyon which contains the communities of Vincent, Acton, Ravenna, and Agua Dulce.