428 B. WILLIS — SOME COAST MIGRATIONS. CALIFORNIA 



immediate coastline. A broad lowland borders tbe ocean about Santa 

 Barbara, extending from the shore to the steeps of tbe adjacent coast 

 range. Although elevated from 40 to '200 feet or more above sea, although 

 traversed by incised streamways, although built up by alluvial cones 

 from the mountain ravines, and in general modified by various subaerial 

 agents, the lowland represents a plain of submarine origin. It is a sec- 

 tion of sea-bed elevated slightly above sea. In the development of its 

 dominant slope marine conditions controlled, whereas deformation and 

 erosion only subordinately affected its present attitude and detail. This 

 is the first of the three t3 r pes referred to. 



From Port Harford to point Buchon the San Luis range stretches near 

 the coast. At its foot is a marked marine terrace, which fronts the im- 

 mediate shore with sea cliffs from 20 to 80 feet in height and in places 

 attains a width of half a mile. Being a wave-cut bench topped by 

 coarse conglomerate, probably of Pleistocene age, this terrace belongs to 

 the first type of coastal slope already described. From the back of the 

 terrace the mountains rise 2,000 feet or more in spurs, between which 

 are deep V-shaped ravines. The horizontal contours of the relief are 

 those of softened maturity. The spurs are rounded, the ravines are 

 acute. The contour curves are convex toward the sea and form sharply 

 reentrant angles landward. Seen against the sky the profiles of the 

 spurs are in agreement with the maturity of contours in general, but in 

 detail they are marked by slight terrace facets. Traced horizontally 

 these terraces are so continuous and nearly level that there is no doubt 

 they are terraces of wave erosion. The most conspicuous one is approx- 

 imately 700 feet above sea. The history of this coastal slope of the San 

 Luis mountains is one of subaerial erosion, transient submergence, and 

 emergence. The dominant activity by which it was sculptured was 

 erosion. Marine erosion was a very subordinate influence. Deforma- 

 tion has had no effect upon its form, except as it has modified the con- 

 ditions of the other two activities. This is the second of the three types 

 of coastal slopes. 



A third type is thought to be exemplified on the coast from point Sur 

 to Piedras Blancas, and perhaps most strikingly at Gamboa point. The 

 steep front which this coast presents oceanward has been described. 

 Considered in a broad way, its horizontal contours are gentle curves, 

 which are concave seaward and meet in prominent angles that are 

 capes. The shoreline on the accompanying map illustrates this form, 

 which, however, in detail is modified by the canyons cut across the 

 scarp. Landslide benches and scarps and remnants of marine terraces 

 are subordinate features of the slope. As has already been stated, this 

 steep may have been either a sea-cliff or a fault scar]). 



