BULL. QEOC. SOC AM. VOL. 11, 1899, PL. 25 MAP OF SANTA LUCIA RANGE, CALIFORNIA, AND ADJACENT FEATURES Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/11/1/417/3383257/BUL11-0417.pdf by guest on 24 September 2021 BULLETIN OF TH E GEOLOGICAL SOCIETY OF AMERICA SOME COAST MIGRATIONS, SANTA LUCIA RANGE, CALIFORNIA BY BAILEY WILLIS ( Read, before the Society December 27, and before the Cordilleran Section December 29, 1899) CONTENTS Page Introductory note.......................................................................................................... 417 The present scene......................................................................................................... 418 Pre-Franciscan history ............................................................................................... 419 Coast complex........................................................................................................ 419 Pre-Franciscan erosion ........................................................................... 419 Franciscan history .. ■........................................... ............................ ............... 420 Franciscan stratigraphy....................................................................................... 420 Franciscan geographic conditions................................................................ 420 Nature of deformation..................................................................................... .. 420 Post-Franciscan history............................................................................................... 421 Cretaceous land...................................................................................................... 421 Miocene (?) stratigraphy...................................................................................... 422 Geographic conditions of the Miocene (?)......................................................... 422 Relation of the Miocene (?) and Miocene strata............................................. 423 Pine Mountain section; Franciscan to Pliocene............................................. 424 Pliocene to present....................................................................................................... 425 Physiography of the coastal slope...................................................................... 425 Three types of coastal slopes................. - .................. ........................................ 427 Incidents in the scarp-growth................. ............................................................ 429 Summary......................................................................................................................... 430 Explanation of figure 2 ............................................................................................... 431 I ntroductory N o t e The following article presents observations made during a trip from Monterey to San Luis Obispo along the intervening Coast ranges. I was accompanied by Doctor H. W. Fairbanks, in whose articles many of the facts herein presented have already been published,* and I am indebted to him not only for pointing out the most interesting and significant »Stratigraphy of Slate Springs. Amer. Geologist, vol. xviii, 1896. LX—Boil. Geol. Soc. Am., Vol. 11, 1899 (417) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/11/1/417/3383257/BUL11-0417.pdf by guest on 24 September 2021 418 B. WILLIS— SOME COAST MIGRATIONS, CALIFORNIA phenomena of the region, but also for helpful discussion of their inter­ pretation. Professor A. C. Lawson * has described the geology of Cartnelo bay just south of Monterey, a district which adjoins on the north that herein referred to and which includes the Santa Lucia granite, the youngest member of the Coast complex hereafter defined. My observations are in general in accord with those made by Lawson at Carmelo bay and by Fairbanks farther south. T h e p r e s e n t S cene Point Sur, a prominence of the California coast, lies 24 miles south of Monterey. From it the coast stretches 57 miles southeast to Piedras Blancas. Along this section extends the westernmost of the Coast ranges, locally known as the Santa Lucia range, which attains elevations of 4,000 to 5,000 feet. The mountains present a bold front to the ocean, precipitous, it is true, only near sealevel at isolated promontories, but generally steep. Ravines gash this front deeply. In general, the aspect of the mountain slope is that of mature topography. In detail, there are variations of form significant of successive episodes of uplift. Near Slate Springs, 35 miles southeast of point Sur, there are two basal conglomerates—the one, that which is being formed by the waves which now dash against the rocky shore; the other, that which was similarly formed when they broke on a shore of Mesozoic date. The present conglomerate is the beach; the older conglomerate is the base of the Franciscan or Golden Gate series, and rises in cliffs several hun­ dred feet above the beach, the strata dipping 70 to 80 degrees to the southwest. The present conglomerate and the older one both consist largely of pebbles and boulders of a still older complex, which will be called the Coast complex. On the summit and eastern flank of the Santa Lucia range occur strata which are much younger than the Fran­ ciscan formation. They constitute a group whose members bring the record down to late Neocene (Pliocene) time. The sequence thus briefly indicated includes (1) the development of the Coast complex; (2) profound erosion of the Coast complex; (3) deposition of the Franciscan conglomerate, sandstone, and shale; (4) oro- genic movements, which resulted in deformation of the Franciscan forma­ tion ; (5) erosion of the Coast complex and Franciscan rocks, which is partially represented in later sediments; (6) evolution of the present mountain system and coastal front. ♦ The Geology of Carmelo bay. University of California, Bull, of the Dept, of Geology, vol. i, p p . 1-50. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/11/1/417/3383257/BUL11-0417.pdf by guest on 24 September 2021 PRESENT SCENE AND PRE-FRANCISCAN HISTORY 4 1 9 The history is a long one, extending from possibly the Paleozoic period to the present, and a very complex one, comprising the phenomena of sedimentation, erosion,metamorphism, orogeny,and perhaps epeirogeny. P r e -F ranciscan H istory COAST COMPLEX The Coast complex consists of crystalline rocks, chiefly metamorphic, including marble, quartzitic schists, mica-schists, gneisses, and granite. The granite is intruded in the others and did not share their experience of profound metamorphism. The marble and schists constitute a sedi­ mentary series. The gneisses may in part or whole have had an igneous origin. The whole has suffered deformation in a deep zone of flow, re­ sulting in structural and mineralogical changes which to a great extent obscure the original characters of the rocks. Fairbanks * has described the series somewhat in detail under the name “ basement complex.” This term is aptly applied, as the Coast complex is the intricate mosaic at the base of the geologic column in the Coast ranges. The age of the Coast complex can only be vaguely guessed. It is long pre-Cretaceous; it may probably be Paleozoic. The former statement follows from the age of the succeeding Franciscan rocks, which are either Eo-Cretaceous or Jurassic. The Paleozoic date is an inference on the uncertain grounds of lithologic and structural similarity to the meta­ morphic complex of the Sierra Nevada. The oldest rocks of the Coast complex were sediments, either calca­ reous muds or quartzose sands. The region of their accumulation was therefore marine, but not so remote from land as to escape terrigenous deposits. Land was probably near, since the sediments were buried to that depth which conditions deformation-by-flow and recrystallization, and zones of such great accumulation of sediment are usually shore zones. PRE-FRANCISCAN EROSION Pebbles of gneiss and granite from the Coast complex chiefly compose the basal Franciscan conglomerate. These rocks had become surface rocks at the inception of the Franciscan epoch. The elevation of the folded and schistose gneisses from the zone of deformation-by-flow in­ volved orogenic or epeirogenic movements vertically of great amount, and corresponding erosion of the mass. Thus in some pre-Cretaceous epoch a land area succeeded to the sea in this region, and in Franciscan time its shore closely approximated the position of the present shore. ♦ Review of our knowledge of the geology of the California Coast ranges. Bull. Geol. Soc. Am., vol. 6, pp. 7&-82. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/11/1/417/3383257/BUL11-0417.pdf by guest on 24 September 2021 420 B. WILLIS— SOME COAST MIGRATIONS, CALIFORNIA The sediments resulting from the erosion of that land have not been discovered; only the fact of a great hiatus in the record is obvious at the unconformity. F ra nciscan H istory FRANCISCAN STRATIGRAPHY The basal conglomerate of the Franciscan series is a very coarse shore deposit composed of pebbles and boulders up to two or more feet in diameter in a sandy matrix. The materials were derived from the im­ mediately adjacent Coast complex upon which the conglomerate was deposited. The strata exposed in the mountain slope are strikingly like the deposits which constitute the beach at the base of the cliffs,