430 B. WILLIS — SOME COAST MIGRATIONS, CALIFORNIA 



of 100 feet or more in altitude, and occurring at Posts 800 to 900 feet, at 

 Devils canyon possibly 1,000 to 1,100 feet, and at point Buchon approx- 

 imate! y 700 feet above sea. Their elevation at Posts is read from con- 

 tours of Coast Survey chart number 5470. The other altitudes are based 

 on aneroid readings of uncertain value. These terraces are more 

 strongly marked and more generally present than any above or below 

 them, and they have been correlated by Doctor Fairbanks with a gen- 

 eral elevation of hill summits about San Luis Obispo and throughout 

 an extensive area of the adjacent district. 



Along the base of the scarp extend stretches of terrace now elevated 

 40 to 80 feet above sea, which are covered with heavy gravel deposits 

 and are tentatively referred to the Pleistocene. No more definite date 

 has yet been determined for them. 



Between themonadnock, Cone peak, and the marine bench now being 

 cut in the base of the scarp, there is thus a physiographic record of the 

 uplift of the Santa Lucia range. The history covers Pliocene and Ple- 

 istocene time to the present. Marked features of the physiography are 

 the high monadnocks, the upper dissected plain at 3,200 feet above sea, 

 the lower dissected plain and correlated terraces at 700 to 1,000 feet 

 above sea, and the Pleistocene terrace ; but the most striking physio- 

 graphic feature is the great fault-scarp, if such be its true character, 

 dividing the upraised mountain block of the Santa Lucia range from, 

 the downthrown mass of the western land, which is submerged beneath 

 the Pacific. 



Future observers will trace out relations between the various physio-, 

 graphic features and the marine and fresh- water deposits of post-Miocene 

 age. The sedimentary and physiographic records are both fairly con- 

 tinuous and legible in the interior valleys as well as along the coast, and 

 will yield a connected history of the Coast ranges when studied in detail 

 with adequate maps. 



Summary 



The outline of the history since the earliest geologic conditions re- 

 corded is summarized in the accompanying diagram ; but one salient 

 fact needs here to be emphasized : Along this farthest Pacific margin of 

 the continent the present coast occupies a position across which coasts 

 of earlier ages have repeatedly migrated, as. land or sea for the time 

 being prevailed. The student of continental growth finds no evidence 

 of permanent encroachment of continent or ocean either upon the other. 

 The student of mountain growth, however, finds an example of the gen- 

 eral law that the site of an existing mountain range has been occupied 

 in past ages by successive generations of mountain ranges. 



