The coast of southern California is composed of low sea cliffs bordered by terraces and a few coastal plains and deltas. Blocks form projections into the sea and feature a series of raised terraces such as those at Point Loma, Soledad Mountain, and the San Pedro Hills in the Los Angeles area.
North of Los Angeles, the Santa Monica Mountains follow the coast. Sea cliffs in this area are actively eroding, particularly in areas where they have been cut into alluvium. At Point Conception, the coast trends north-northwest and a different geomorphology is evident. Despite the presence of a series of mountain ranges that cut across the coast, the rugged central and northern California coast is one of the straightest in the world. This area has high cliffs with raised marine terraces. A few broad river valleys interrupt the mountainous coast. Here, river sediments have been returned by the waves to the beaches and carried inland by westerly winds to form some unusually large dune fields.
North of Cape Mendocino, the coast trends almost directly north, through Oregon and Washington, to the Strait of Juan de Fuca. Along this coast, lowland valleys at the mouths of large rivers alternate with short, relatively low mountainous tracts. Barriers or spits have formed at river mouths, as have large dune fields. Many of the rivers, including the great Columbia, discharge into estuaries.