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Home , California Coast Ranges, Pilarcitos Creek, Purisima Formation, San Gregorio Creek, San Lorenzo River

DESCRIPTION OF THE SANTA CRUZ QUADRANGLE.

By J. C. Braimer, J. F. Newsom, and Ralph Arnold.

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INTRODUCTION. allelism is less marked, or is absent, in the minor Drainage. The streams on the northeast side of tion of the geologic events, as recorded in the rocks, relief. The main ridge of the group within the the main watershed flow into the Bay of San Fran­ is made possible by the widespread distribution of Most of the work on the geology of this quad­ area is known as Castle Rock Ridge along the cisco; on the west side they descend directly into certain geologic bench marks, such as characteristic rangle was done during the summer months of boundary between Santa Clara and Santa Cruz the Pacific Ocean. The largest hydrographic basin faunas and formations. Correlations between the 1892 to 1904. During that time much assistance counties, but the same ridge toward the northwest in the quadrangle is that of , Ranges and other geologic provinces, the was received from the instructors and the students corner of the quadrangle is known as Cahil Ridge. which enters the ocean at Santa Cruz and has a for instance, are extremely difficult in Leland Stanford Junior University. This ridge is situated nearer to the Santa Clara drainage area of 126 square miles. The next and hazardous because the history of each province The work has at all times been done under the Valley than to the sea; it runs southeast and north­ smaller hydrographic basins are those of Pescadero is more or less distinct, though obviously related in personal direction of Mr. Branner or Mr. Newsom. west across the entire quadrangle and is the main Creek, with an area of 60 square miles, and San regions of juncture. . Most of the work in the region watershed of the range. It forms an escarpment Gregorio Creek, which has an area of 52 square The Santa Cruz quadrangle is characteristic of ' has been done by Mr. Branner or under his imme­ with a steep northeastern slope, bordered by the miles. The mouths of these two streams are sepa­ the Coast Ranges in general as regards geologic diate direction. Mr. Newsom has directed the line of valleys lying along the rated by only 4 miles of coast. formations and, in a measure, topography as well, work in a large part of the region west of line; to the southwest, from the ridge's summit the The streams on the west side of the range have but in respect to vegetation and certain features of the Stevens Creek fault. The diabase area near general slope of the country toward the ocean is cut back rapidly into the soft sediments which form topography dependent on the humidity of the Langley Hill was mapped chiefly by Mr. Arnold, comparatively gradual, though the region is cut by the mass of the mountains, so that the lower parts region it is quite different from many of the ranges and the descriptions of the petrography of this and many deep gulches, formed by the streams heading of their channels are already fairly well graded. farther south or farther inland. The broader fea­ the other crystalline rocks were written by him. near the watershed and flowing directly to the sea. San Lorenzo River reaches the 500-foot level about tures of the history are the same throughout the Mr. Arnold also mapped the marine Quaternary The highest point in the range within the 2 miles above the town of Boulder Creek that is, coastal belt, however, so that the descriptions fol­ and terraces. The description of the Purisima area of the map is Stanford Peak, on Castle Rock about 16 miles from the mouth of the river. San lowing may be applied in general to the whole formation is in part by Mr. Arnold and in part by Ridge, 4 miles southwest of Saratoga; it. has an Gregorio Creek reaches the 500-foot level about 9 region from south to the region of Mr. Newsom. All paleontologic work, except where elevation of a little more than 3200 feet. Both miles from its mouth, while the 500-foot level on northern Santa Barbara County. otherwise specified, has been done by Mr. Arnold. east and west of this point many of the main peaks is reached about 14 miles above its ROOKS OF THE QUADRANGLE. rise higher than 2000 feet, and several are more mouth. The larger streams west of the range GEOGRAPHY. than 2500 feet in height. San Loreuzo, San Gregorio, Pescadero, and Wad- Sedimentary rocks, consisting of conglomerates, Little relation is apparent between the topo­ dell creeks are all perennial. sandstones, and shales, of pre-, Creta­ Location. The Santa Cruz quadrangle proper graphic features of the quadrangle and the geologic East of the main watershed the basins of the ceous, Tertiary, and Quaternary age, are exposed lies between latitudes 37° and 37° 30' north and structure. Exceptions to this rule may be noted, streams flowing into the Bay of San Francisco are in the Santa Cruz quadrangle, the relative areas of longitudes 122° and 122° 30' west, but a strip of however, in the cases of Ben Lomond Mountain, smaller than those west of the range. The largest which are shown on the map. There are also two country south of latitude 37°, around the town of Butano Ridge, and Castle Rock Ridge, and of the of them are the basin, with occurrences of diorite of importance and some minor Santa Cruz, is shown on the maps and covered by valleys along certain of the important fault lines. an area of 37 square miles, and the Stevens Creek areas of schist and limestone. In addition, dia­ the descriptions of this folio, because it is too small Ben Lomond Mountain has been formed by the basin, with an area of 28 square miles. bases, lavas, and tuffs are of considerable impor­ to form a quadrangle by itself. The whole area is upward tilting of a granitic block along the Ben The largest streams on the east side of the range tance in the central part of the quadrangle and in here referred to as the Santa Cruz quadrangle. Lomond fault, forming a mountain with a sharp are Stevens Creek, San Francisquito Creek, and the region adjacent to Stanford University. Small The total land area shown on the map is 712 escarpment toward the northeast and a long, gentle Campbell Creek. These streams are perennial only areas of travertine are associated with the latter square miles; the water area, including that in a slope toward the southwest. Butano Ridge is an in their upper portions. In summer and autumn rocks locally. strip 4 miles wide extending east and west across anticlinal ridge formed by massive sandstone, the they disappear soon after they emerge from the The formations above the basement complex the quadrangle south of latitude 37°, covers 332 axis of the Butano anticline, a northwest-southeast foothills upon the plain, the water entering the of granitic rocks, schists, and limestone consist of square miles. Near the northeast corner of the flexure, being parallel with and about one-fourth gravels that underlie the Santa Clara Valley. the following: Franciscan, probably of upper quadrangle is the southeast end of the Bay of San mile north of the axis of the ridge. In its more The water from a portion of the San Francis­ age; Knoxville, Lower Cretaceous; Chico, Francisco, covering an area of 15 square miles. prominent part Castle Rock Ridge is formed by quito is caught in Searsville Lake. Upper Cretaceous; limestone inclusions of Eocene The quadrangle is situated entirely in , massive sandstone which has been compressed into To the northwest, near the north boundary of age; Butano and San Lorenzo, Oligocene; Vaque­ and includes parts of four counties San Mateo, sharp anticlinal and synclinal folds immediately the quadrangle and in the San Audreas fault valley, ros, lower ; Monterey, middle Miocene; Santa Cruz, Santa Clara, and Alameda. west of the San Andreas fault. The lines of the is Crystal Springs Lake, from which San Francisco Santa Margarita, upper Miocene; Purisima, upper Relation to Coast Range and Pacific Ocean. major faults of the quadrangle, viz, the Butano draws a part of its water supply. Miocene to middle Pliocene; Merced and Santa The part of California in which the Santa Cruz fault, the Ben Lomond fault, and the San Andreas Where the streams debouch upon the plain of Clara, upper Pliocene and lower Quaternary; and quadrangle lies is commonly known as the Coast fault, are marked by more or less continuous val­ Santa Clara Valley they are characterized by broad Quaternary deposits. Of these the most important Ranges. This region is characterized by a series leys. Some small valleys also have their directions alluvial fans of such low relief that their form can are the Franciscan, Knoxville, Chico, Butano, of parallel mountains and valleys that follow the controlled by the San Gregorio fault. hardly be more than suggested by the 100-foot Vaqueros, Monterey, and Purisima. char­ Pacific coast from 35° to about 41° north latitude, The areas in the quadrangle underlain by the contour interval of the topographic map. San acteristic of the various formations in the quadrangle just north of Cape Mendocino. These mountains formations from the Quaternary down to the base Francisquito Creek flows along the crest of a ridge are figured on illustration sheet 2. The following and valleys have a general direction of N. 40° W. of the Purisima are usually characterized by well- that has been built by its alluvial deposits. To description will take up the different formations in Southeast of San Francisco the Coast Ranges are rounded hills and evenly sloping valleys. The one looking along the Southern Pacific Railroad the order of age, beginning with the oldest beds. divided by the Santa Clara-San Benito Valley hillsides are generally covered with a deep coating track toward that stream from either Menlo Park into two well-defined groups the Mount Hamil­ of soil, and cliffs are rarely'found on them. An or Palo Alto station it is evident that the grade rises METAMORPHOSED SEDIMENTARY ROCKS. ton division of the , standing between unusual feature of the topography is the exceeding toward the creek. Two series of metamorphosed sedimentary rooks the Santa Clara Valley and the San Joaquin Val­ steepness of many of the soil-covered hillsides, An area of marshy lands borders the Bay of San are exposed in the quadrangle one the Francis­ ley, and the Santa Cruz Range, standing between slopes of 35° to 40° being not uncommon. In one Francisco at the northeast corner of the quadrangle, can formation, the other of probably pre-Franciscan the Santa Clara Valley and the ocean. place a soil and vegetation covered hillside with a and very small and insignificant areas of marsh land age. The supposed pre-Franciscan metamorphic The quadrangle takes in the full width of the slope of 50° from the horizontal was observed. occur where some of the larger streams enter the rocks are confined to the region of the Ben Santa Cruz Range, and includes also a part of the With the exception of the area immediately around sea along the Pacific coast. Lomond quartz diorite batholith and probably owe Santa Clara Valley and the south end of the Bay of Black Mountain and Congress Springs the foothills their alteration to the intrusion of that igneous San Francisco, while its western and southwestern of the range east of the San Andreas fault have DESCRIPTIVE GEOLOGY. mass. The metamorphosed Franciscan formation well-rounded outlines. In the northeastern portion parts extend out over the Pacific Ocean. The GEOLOGIC OUTLINE. is found in the Black Mountain area and in the belt Santa Cruz Range crosses the quadrangle in a of the quadrangle is a gently sloping plain extend­ which extends both northwest and southeast of the southeast-northwest direction. Northwestward the ing from the foothills to the marshes bordering San The California Coast Ranges are young, geolog­ latter. There are also a few cases of local metamor- range narrows and disappears at the coast a few Francisco Bay. ically speaking, yet their history is complex. In phism of the Monterey shale by intruding diabases, miles south of San Francisco; southeast of the The Monterey shale areas are usually character­ other portions of California and Nevada there are but these are unimportant. quadrangle it forms the watershed between the ized by steep, narrow V-shaped canyons and high , , , , and Santa, Clara-San Benito and Salinas valleys, though ridges with steep slopes, while the massive sand­ Jurassic rocks; the oldest rocks in the Coast Ranges SUPPOSED PRE-JURASSIC ROCKS. cut in two by near Sargents. Beyond stone beds of the Vaqueros and Butano formations of which the age is definitely known are Lower SCHIST AND LIMESTONE. thatTiver it is locally known as the Gabilan Moun­ generally produce a comparatively rugged topog­ Cretaceous. Above the basement complex of acidic Distribution. Northwest of Santa Cruz there are tains, and still farther southeast it merges into the raphy with occasional prominent cliffs. The granite plutonic rocks and metamorphic schists and lime­ isolated patches of micaceous schist and highly main Diablo Range about the headwaters of San area of Ben Lomond Mountain in its more elevated stones, the age of which is uncertain, there are crystalline white limestone or marble, lying above Benito River. portions also produces a rugged topography. represented within the Santa Cruz quadrangle alone the quartz diorite mass that makes up the core of Filled U-shaped valleys are developed in many fourteen recognizable formations. Nine distinct Ben Lomond Mountain. The schist and the lime­ TOPOGRAPHY. places along the sea coast. The valleys in the and far-reaching disturbances, as recorded by pro­ stone are interbedded in some places, notably in the Relief. The parallelism of the valleys and ridges more elevated portion of the quadrangle, however, found unconformities, not to mention many local quarries and along the road to the summit of Ben so characteristic of the Coast Ranges as a whole is are V-shaped. Finely developed sea terraces occur readjustments, took place in the region during the Lomond Mountain, 2 miles west of the town of Fel- less apparent in the minor topography of the Santa along the coast from the mouth of Pescadero Creek deposition of these formations. Volcanism was ton. The limestone areas are much smaller than Cruz quadrangle. Some of the larger valleys and to Santa Cruz, and less clearly defined terraces are active during several epochs, and in at least one the schist areas around them. The schist usually ridges are parallel with one another and with the found along the coast northward from the mouth of these lasted for a considerable time. Between occurs between the limestone and the quartz diorite, main system of Coast Range ridges, but this par­ of Pescadero Creek. different areas within the Coast Ranges the correla­ and the latter is apparently younger than either the schist or the limestone. The relations of the schist north. G. D. Louderback and Ralph Arnold, act­ the latter in fine needles forming a compact dynamic and of contact origin, are common, is any and the limestone to the underlying quartz diorite ing as a committee to harmonize the mapping of groundmass in which are embedded rectangular glaucophane schist known; and there, too, exten­ and overlying sedimentary rocks are shown in sec­ the two areas, held to the theory that the disputed prisms of lawsonite. Sphene and talc are also sive masses of peridotite occur, and altered sedi­ tion G-G on the structure-section sheet. The schist beds were of Franciscan age, and their decision was present, but neither garnet nor epidote occurs in ments of the same chemical character as in the and the limestone have been much broken up and accepted tentatively for present mapping purposes. any quantity in this type. This schist occurs on Coast Ranges, but of totally different petrographic disturbed, apparently by the intrusion of the quartz Character. The formation is characteristically the Hellman ranch, 3 miles west of Redwood. character. Altered quartzites are abundant in the diorite. It seems probable, therefore, that they are metamorphic, although large areas of unaltered (#) Quartz-glaucophane-lawsonite schist, similar Sierra Nevada, also altered clay shales and altered older than the underlying quartz diorite and that rocks are found within it. It consists of sandstone, to the last, but more acidic, and' containing in diabase tuffs; but the quartzites have been changed they owe their metamorphism in part at least to the shale, limestone, chert, schist, and gneiss. It is addition to the quartz and other constitutents the to sericite schists, the clay shales to andalusite intrusion of the quartz diorite mass. This view of associated at many places with serpentine, which greenish mineral carinthine. Found near the schists, and the diabase tuffs and the peridotites to their relations is borne out by the facts in other por­ intrudes it in the form of dikes and large masses. Schrader farm, 2 miles west of Redwood. amphibolites, all without glaucophane. What is tions of the Coast Ranges. No fossils have ever been The sandstone as a rule is moderately fine (c) Actinolite schist, of which the principal con­ more puzzling, the metamorphism in the Sierra found in the limestone or the schist, the age of which grained, although it is sometimes coarse and occa­ stituents are chlorite and the green prismatic Nevada and that in the Coast Ranges seem to have is therefore unknown. They appear from their sionally even pebbly. Its color is gray, weathering actinolite known as smaragdite. Glaucophane is been contemporaneous. extreme metamorphism, however, to be older than to brown, and it is usually characterized by small also present in varying amounts, as is also carin­ Age. No identifiable fossils have been found in the Franciscan formation, though the latter has not bits of hardened shale included in it. Quartz is thine, while titanite is common and in many places the Franciscan formation, but in the Knoxville been seen in contact with them. the principal constituent, but mica, hornblende, abundant. This type occurs near the Hopkins beds, which unconformably overlie it throughout

Character of / the schist. Weathering

Three other faults of importance have been most important of these is the Butano anticline, which CRETACEOUS TIME. lava, and in the bottom fossiliferous sediments were traced the Ben Lomond fault, the Butano fault, is well defined from the northwest end of Butano found in the cracks of the eruptive. Near the and the Zayante fault. In the first two of these Ridge to Lompico Creek, a distance of 18 miles. So far as we now know, Cretaceous time is ancient crater the lava is 400 feet thick; where it is the downthrow is on the northeast side of the The later Tertiary formations that border the represented in this quadrangle only by rocks of cut through in a well on Menlo Heights its margin fracture, while in the Zayante fault the downthrow coast line from Santa Cruz to Halfrnoon Bay, Knoxville and Chico age. The Knoxville sedi­ is only 20 feet thick. is on the southwest side. the Monterey and the Purisima, are generally but ments are conglomerates, sandstones, and shales. These lavas, and indeed the craters themselves, The Ben Lomond fault skirts the east and north slightly folded. In a general way the beds of The abundance of pebbles of jasper and eruptive sank slowly beneath the Miocene sea and were soon sides of Ben Lomond Mountain for a distance of these formations dip gently toward the sea. (See rocks in the Knoxville basal conglomerates shows afterward covered by sediments mingled with the 15 miles, and is the fracture along which the Ben sections E-E, F-F, and G-G.) that the land areas were to a considerable extent shells of marine mollusks. Lomond Mountain block was tilted up. (See sec­ The axes of the folds lying between Ben Lomond made up of Franciscan eruptives and jaspers. Post-Monterey uplift. The next event of impor­ tions E-E, F-F, and G-G.) At its southeast end Mountain and the Butano fault and its southeast­ Facts gathered through the Coast Ranges suggest tance was the uplift of the submerged area. This the displacement is only a few hundred feet, but at ward continuation pitch to the southeast, as is that during the time of the deposition of the was accompanied by much folding, faulting, and the north end of Ben Lomond Mountain the dis­ plainly shown by the areal geology map and cross Knoxville beds the region now lying between the crushing in the region near Cahil and Castle placement appears to be over 2000 feet. To the sections D-D to G-G. The axes of the chief folds Sierra Nevada and the ocean was a sound or series Rock ridges and between Ben Lomond Mountain uptilting of the Ben Lomond block at the east and between the Butano fault and Castle Rock Ridge, of sounds containing islands a region somewhat and Castle Rock Ridge, but the region southwest north is due the bold escarpment of that mountain Mindego Hill, and La Honda pitch to the north­ like that along the present southern coast of of the Ben Lomond fault was not much folded at on those sides, and likewise its comparatively long west, as shown in sections C-C to F-F. Along the Alaska and British Columbia, About the islands this time. During this period many diabase intru­ and gentle slope toward the southwest. southwest slope of Ben Lomond Mountain is a and along the shores the pebbles and bowlders of sions occurred along the line of the main dividing- The Butano fault lies immediately northeast of monoclinal fold, the axis of which is approximately the conglomerate beds were worn and deposited, ridge, those of most importance being near Langley Butano Bidge through its entire extent. (See horizontal. In the northern portion of the quad­ and subsequent depressions were followed by and Mindego hills. The Monterey or post-Mon- sections D-D, E-E, and F-F.) It crosses San rangle (except in the Purisima area, noted above) deposits of sands and clays. terey uplift was followed by a considerable period Lorenzo River 5^ miles north of the town of Boul­ and in the region of the older rocks lying immedi­ of erosion. TERTIARY TIME. der Creek. Thence it appears to follow a highly ately east of the San Andreas fault, the structure of Purisima subsidence. The post-Monterey erosion crushed belt of the San Lorenzo strata, toward the the Tertiary and older rocks is obscure and the The Tertiary strata appear to rest unconformably was followed by a subsidence, during which the southeast. Pescadero Creek has cut out its valley positions of the axes of the folds occurring there upon all older strata in the quadrangle, and an ero­ Purisima sediments were deposited along a sinking along the crushed zone of the Butano fault from its are not known. sion interval and deformation must therefore have shore, forming an overlapping series. This over­ headwaters to the northwest end of Butano Ridge. Movements in the nature of uplift or depression occurred between Cretaceous and Tertiary time in lapping of the older sediments by the newer ones The Butano fault cuts diagonally across the region with little or no deformation took place at various this area. toward the ancient shore line is especially notice­ lying between the San Andreas and the San times. These are treated under the next heading, With the exception of the diatomaceous shale, able in the region north and northwest of Purisima Gregorio faults, and approaches both of those frac­ "Geologic history." which was probably formed in comparatively deep Creek. The extent of the Purisima subsidence is tures at an acute angle. The downthrow is on the Metamorphism has affected the Franciscan for­ and clear water, the Tertiary sediments of the quad­ unknown. It seems probable, however, that the north side of the fracture, and where the fault mation through its entire range, but the causes rangle consist of sandstone, conglomerate, clay Purisima sediments never extended far beyond the crosses San Lorenzo River the displacement appears of this metamorphism and its exact character are shale, and gravel. These deposits indicate near- present mapped limits of that formation. Had they to be over 2000 feet. little known. This subject is discussed more shore conditions, and the thickness of the Tertiary formerly extended over the entire region, it seems The Zayante fault extends from a point near the fully in the section relating to the Franciscan strata indicates a plentiful supply of sediment. At almost certain that outliers of Purisima strata would town of Boulder Creek slightly south of east to the formation (p. 2). least three uplifts with accompanying folding, be found far removed from the main areas. The eastern edge of the quadrangle, in the valley of faulting, and erosion, followed by subsidence, conclusion is therefore drawn that Cahil and Castle . (See section G-G.) The crushed GEOLOGIC HISTORY. occurred during the Tertiary. Rock ridges, Ben Lomond Mountain, Butano Ridge zone along this fracture is exposed along Love, At the beginning of Tertiary time land masses and adjacent ridges, and at least a part of the region PRE-FRANCISCAN TIME. Newell, and Lompico creeks and the north fork of were probably in existence northeast of the San lying southwest of Castle Rock Ridge were above Zayante Creek. The dovrathrown block is south­ The oldest rocks exposed in the Santa Cruz Andreas fault, southwest of the San Gregorio fault, sea level, in part at least, during Purisima time. west of the fracture. Data for the estimation of the quadrangle appear to be the schist, white marble, and southwest of the Ben Lomond fault. Whether The main lines of the ranges in the Santa Cruz displacement are lacking; but the crushed and dis­ and other metamorphosed sedimentary rocks which these areas were islands or were connected with a quadrangle therefore appear to have been fixed in turbed nature of the strata along the line of fracture lie upon the quartz diorite in the region northwest large land mass is not known; they must have pre-Purisima time. indicates that the movement has been considerable. of Santa Cruz. The age of these rocks is unknown; been of considerable size, however, to supply the During at least a part of the post-Monterey it is safe to say, however, that they are very old, great thickness of sediments which was derived period an arm of the sea, in which unique con­ FOLDS. and may have been deposited in Paleozoic or pre- from them. An arm of the sea or an embayment ditions were prevalent, occupied what is now the As has been remarked, the folding over much of Paleozoic time. They are believed to be older extended between these three land areas. In this Salinas Valley, south of , and extended the quadrangle has been intense and in many places than the Franciscan, though in the Santa Cruz body of water limestone of Eocene age, the Butano north into the Santa Cruz quadrangle as far as it is impossible to determine the structure in detail. quadrangle no Franciscan rocks are found lying sandstone (supposed Oligocene), the San Lorenzo Boulder Creek. The sediments laid down in this The major folds, however, have their locations and upon them. It seems probable that after these shale (Oligocene), and the Vaqueros sandstone bay are termed the Santa Margarita formation, and characters shown in the cross sections. They have strata were deposited in the sea they were intruded (lower Miocene) were deposited, all (except possibly probably represent late middle Miocene time. The practically parallel axes with a general direction of by the quartz diorite mass which makes up Ben the Eocene) in conformable sequence. relation between this bay and the waters in which about N. 60° W. These axes of folding are nearly Lomond Mountain, and were greatly disturbed and Post-Vaqueros uplift. After the deposition of the lower portion of the Purisima were deposited is parallel with the lines of the minor faults (the metamorphosed. This intrusion is therefore believed the Vaqueros sandstone at least a portion of the not known. Zayante, Butano, and Castle Rock Ridge faults), to be the second important event of which there is region appears to have been raised, and was proba­ Post-Purisima uplift. At the end of Purisima but they are cut across diagonally by the San a record in the quadrangle. bly folded and faulted; in parts of the area consid­ time occurred an uplift which appears to have been Andreas, the San Gregorio, and a part of the Ben After the intrusion of the quartz diorite an erable erosion appears to have taken place. accompanied by little intense folding. The Puri­ Lomond faults. uplift occurred and most of the metamorphosed Pre- Monterey subsidence. After the lower sima beds generally, while considerably faulted and The older rocks of life quadrangle are invariably sediments were removed, leaving only a few rem­ Miocene erosion a subsidence occurred, causing the folded, have not been subjected to the great folding much more crushed and folded than the newer, and nants of limestone and schist. How long this region between the San Gregorio and San Andreas and crushing which the pre-Purisima rocks have there is little doubt that folding and faulting have erosion interval lasted is unknown. The rocks faults to sink beneath the sea. It is possible that undergone. been going on more or less continuously since pre- deposited upon the quartz diorite and metamorphic the area west of the San Gregorio fault also sank It is possible that the adjacent land areas were Cretaceous time. But little is known of the axes rocks are of Tertiary age; a hiatus and an uncon­ beneath the sea at this time. During this period of worn down nearly to base level during Purisima of the folds which were produced prior to the Ter­ formity therefore constitute the only record of the submergence the Monterey diatomaceous shale was time. Cahil Ridge presents an even sky line that tiary; whether these were in a general way coinci­ time between the intrusion of the diorite and the deposited over much of the area, indicating that suggests a peneplain surface. The westward slope dent in position with the Tertiary axes is not known. deposition of the Tertiary beds in the region of open-sea conditions prevailed. of Cahil Ridge is somewhat gradual, but is so dis­ Three uplifts with accompanying folding and Ben Lomond Mountain. During this time there was an active volcano in sected that whether or not it is a tilted peneplaned faulting occurred in Tertiary, time. The main The oldest unmetamorphosed rocks resting the region where Langley Hill now stands. The block can not be stated. If reduction toward base- axes appear to have been along the same general against the quartz diorite are massive sandstones of sea on the southwest extended a little east of the level did occur in Purisima time the peneplain then northwest-southeast lines during each of these supposed Oligocene age at the north end of Ben present site of the village of La Honda, The formed was broken up by later faulting, especially periods, but they did not coincide in all cases, as is Lomond Mountain. The Miocene rests upon the volcano was not far from the seashore, and from along the line of the San Andreas, Butano, and seen west of Big Basin and at the west end of quartz diorite and metamorphosed sediments on its this poured out streams of lava, while enormous Ben Lomond faults. Butano Ridge, where the Monterey shale, with a southern and western slopes. This area was there­ quantities of volcanic cinders were thrown into the So far as we know, the most important of these general westward dip, overlaps the upturned edges fore either a land area up to the Tertiary period or air. Some of the cinders fell into the sea, some movements were along the lines of the San Andreas of the San Lorenzo and Butano formations, which else was uplifted and had lost by erosion its pre- fell on the land, and others fell on the shore, where fault zone. On the west side of this fracture, which are folded along northwest-southeast axes. Terdary sediments, except the metamorphic rocks the angular fragments were worn by the waves. extends many miles to the northwest and southeast, The series of Chico strata from the mouth of above referred to. After the cessation of this volcanic activity the dia­ a great block of the region was uplifted. It was Pescadero Creek to Ano Nuevo Point have been * tomaceous silts again began to accumulate over the probably at this time that a partial barrier was folded along northwest-southeast axes, in a general FRANCISCAN TIME. sea floor. formed across the outlet to the sea of the drainage way parallel to the axes of folding of the Tertiary The area of Franciscan rocks exposed in the During probably late Monterey time there was a from the Sacramento and San Joaquin valleys, strata farther east. Santa Cruz quadrangle is too small and the geology volcano in what are now the foothills 2 miles south causing these streams to form an inland fresh-water Fairly well defined folds occur between the crest too complex to afford any clear conception of the of Stanford University. This volcano was near the lake or series of lakes in what is at present San of Castle Rock Ridge and Ben Lomond Mountain. physical geography and history of that period. sea and some of the cinders from its craters fell into Francisco Bay and Santa Clara and adjacent valleys. (See sections E-E, F-F, and G-G.) Castle Rock The rocks of the series jasper, limestone, meta­ the water. A sheet of lava flowed about 3 miles Fresh-water conditions also extended to and partly Ridge itself is made up, in its most prominent part, morphic sediments, and erupt!ves occur in such toward the northwest and stopped near Menlo filled the Sacramento and San Joaquin valleys. of an overturned anticline with an accompanying confusion, so faulted, altered, and decomposed, that Heights. Some of this lava flowed over the bottom Evidence of this fresh-water body is found in the syncline, as indicated on sections E-E and F-F. their sequence has not been clearly made out. of a shallow sea, possibly over mud flats, for in its fresh-water fauna of the gravel, clay, and sand that The strata between the Castle Rock Ridge and the The jasper and limestone are contemporaneous, and movement it gathered up and squeezed into cracks flank the Santa Cruz and Mount Hamilton ranges. Butano fault generally stand at high angles. South­ as the limestone contains the remains of Forami- in its lower side soft mud filled with marine This fresh-water lake in all probability extended west of the Butano fault is a series of anticlinal and nifera the two rocks must be marine deposits laid shells. The excavation for a reservoir on the hill­ southeastward from the Santa Clara Valley to the synclinal folds with northwest-southeast axes. The down in waters of moderate depths. top south of Stanford University was made in the San Benito Valley. It appears probable that 11 during the post-Purisima uplift the west side of the thinner as the bay shore is approached, and com­ from sandstone beds believed to be intercalated with SOILS. fault block east of the San Andreas fault was raised pletely disappear at the edges and in some places to the Monterey shale a short distance below the base and helped to form the watershed between the the landward of the salt marshes. of the Purisima formation. Oil wells bored along The richest soils of the quadrangle are those of inland fresh-water sea and the ocean. the coast west of Santa Cruz, to penetrate at depths the Santa Clara Valley, which are derived from the Fresh-water lakes were extensively formed else­ ECONOMIC GEOLOGY. the strata which bear bituminous rock at their out­ hills adjacent on the southwest and from the under­ where in the Coast Ranges at about this period. crops, failed to develop any commercial supply of lying gravels of Pliocene and Quaternary age. The Such a large lake existed in the middle and upper After its soils the most important geologic oil. Wells have also penetrated the Purisima and Purisima formation generally produces a deep and Salinas Valley, taking the place of the bay in which products found in the Santa Cruz quadrangle are Monterey strata a mile east of the town of Ben fertile soil. This is especially true where the for­ the Santa Margarita formation was laid down. deposits of limestone and bituminous rock. Gold, Lomond, and also the Monterey beds on Oil Creek, mation is made up of fossiliferous impure sandstone petroleum, building stone, road materials, diatoma- almost at the center of the quadrangle, but always and shale, as is the case over most of its area from QUATERNARY TIME. ceous shale, and sand deposits also occur, but these without satisfactory results. Ano Nuevo Bay northward. Where the Purisima Subsidence. At the end of the period of uplift materials are of comparatively little importance. Apparently the most promising locality for pros­ or the Santa Margarita is composed of diatomaceous above referred to, which probably extended well pecting for oil is that along the coast west and shale and very pure sandstone, as is the case north GOLD. into the Quaternary, a general subsidence of the southwest from the outcropping bituminous rock of Santa Cruz, it produces an exceedingly poor soil. region took place, accompanied by faulting and Placer gold has been found in small quantities beds, since those beds pass down under overlying The Monterey shale, being made up almost entirely considerable folding. Probably the faulting at this in the gravels of Stevens Creek and in some of the shale in that region. Wells drilled here, however, of siliceous material, produces a poor and thin soil. time was chiefly along the old lines of weaknesses. small streams on the eastern slope of Ben Lomond failed to find oil, and it is supposed that the oil The soils produced by the Vaqueros sandstone are At this period the gravels which had been formed Mountain, but there is no likelihood of gold being which must formerly have existed in the sandstones usually poor, as that formation is composed for the in the preceding epoch were more or less folded. found in paying quantities at any place in the of the region has been drained off through large j most part of comparatively pure sandstone. The The strip of gravel extending along the line of the quadrangle. fractures which extended from the surface of the shale of the San Lorenzo formation decays readily San Andreas fault from Crystal Springs Lake to shale down to the underlying sandstone. Many and produces good soil, but little of it is cultivated BITUMINOUS ROCK. the west side of Black Mountain halfway across sandstone dikes, some of them of large size, occur for the area covered by this formation is cut by sharp the quadrangle was probably faulted into its The bituminous rock of the Santa Cruz quad­ along the coast in this region. These were formed ridges and deep, narrow ravines. The Butano sand­ present position at this time. rangle is a porous, loose sandstone impregnated from the underlying oil-bearing sandstones, and the stone produces a sandy soil which under cultivation At some places the land area sank from 1500 with asphaltum a petroleum residue. The most larger ones probably represent the channels through I would quickly become impoverished. This area is to 2000 feet lower than it is at present. On Ben important deposits in the quadrangle are those on which the oil from the underlying strata escaped. covered with a dense growth of redwoods and other Lomond Mountain there are undoubted remnants the southwest slope of Ben Lomond Mountain, from timber and underbrush, which thrive in the sandy BUILDING STONE. of wave-cut terraces up to an elevation of 1500 4 to 6 miles northwest of Santa Cruz. The bitumi­ soil. feet, and what are believed to be terrace remnants nous rocks are sandstone beds lying near the base The sandstone and other sedimentary rocks of The soils in the Ben Lomond Mountain and up to as least the 2000-foot level. Whether this of the diatomaceous shale, which is referred to the the quadrangle are usually too soft or too much Halfmoon Bay areas of quartz diorite are thin and depression affected the whole area of the quadrangle Monterey. Most of the sandstone beds which | fractured to make good building stone. Buff sand­ poor, as are also those in the areas of serpentine is not known. immediately underlie or are intercalated with the j stone in the Chico formation similar to that used wherever they occur. In the area of Franciscan The outlets which were being cut down from diatomaceous shale of this locality are more or less | in the buildings of Stanford University occurs near rocks, however, rich soils are often produced by the the inland lakes to the sea prior to this subsidence bituminous. The structure is monoclinal, with a and southeast of Searsville, but the localities are at decay of the limestones, greenstones, and metamor- were submerged and the region of the Santa Clara gentle southwest dip, hence the asphalt-bearing present inaccessible and the stone is not quarried. phic rocks which abound there. Valley and some of the adjacent valleys became strata crop out along the eastern fringe of the The quartz diorite of Ben Lomond Mountain WATER RESOURCES. inland salt-water bodies. diatomaceous shale, and along the sides of the and other areas in the quadrangle might be utilized Uplift and oscillations. At the end of the sub­ southwestward-flowing streams where these have for building purposes, but thus far these areas have The Santa Cruz quadrangle has but few springs, sidence in the Quaternary period uplift again cut down nearly or quite to the bottom of the shale. been too distant from a market and inaccessible, and most of these are small. Some on the east face occurred, and the coast region was in part at least The bituminous rock is being worked rather and no attempt has been made to use the stone. of Castle Rock and Cahil ridges are charged with lifted to a higher plane than it now occupies. extensively at the quarries of the City Street sulphur and soda, at least one group, Congress ROAD MATERIALS. This uplift was by stages, as is attested by the series Improvement Company, 6 miles northwest of Santa Springs, furnishing water for bottling and medicinal of wave-cut terraces exposed at many places along Cruz. Here the bituminous rock bed is almost The west side of the Santa Clara Valley has a uses. During the dry summer season the streams the coast. Following this elevation was a slight horizontal near the tops of the ridges, has a total fairly good road metal in the limestone and chert on the east side of the range become dry, as do also sinking of the shore line, as is attested by the sub­ thickness of 50 feet, and is overlain by 50 to 100 occurring in the Franciscan strata. The hard many of the smaller creeks on the west side of the merged and filled-in valleys which open seaward feet of much-fractured diatomaceous shale. (See fig. nodules of the serpentine masses and the basalt of range. The west side of the range is much better along the coast from Pescadero Creek to Santa 11, illustration sheet I.) While the character of the area south of Stanford University are also used, watered, however, than the east side. The region Cruz. The filled-in portions of the valleys extend the bituminous bed varies somewhat, the following but are not sufficiently resistant to make first-class drained by the headwaters of San Lorenzo River a mile or more up the streams, the distance vary­ section of the bed as exposed at what is known as roads when used alone. Of the materials used the and Waddell and Pescadero creeks is the best ing with the size of the stream. The present the Point quarry will give an idea of its general chert is the best and makes excellent roads. Unfor­ watered portion of the quadrangle. slopes indicate that in some cases these valleys relations in this district: tunately, however, it is of very meager occurrence. This region is kept moist during much of the have been filled to a depth of a hundred feet or summer season by the dense fogs which drift from Section at Point quarry. LIMESTONE. more. Whether the land along the coast is at Feet. the sea up the valleys. In the rainy season the present sinking, stationary, or moving upward is Fractured diatomaceous shale______-______75 Considerable deposits of pure, highly crystallized moist currents pass up these valleys and cause a High-grade bituminous sandstone______30 heavy rainfall around the heads of San Lorenzo not known. In the region about San Gregorio it Low-grade bituminous sandstone.______10 limestone or marble occur on Ben Lomond Moun­ appears to be rising, as the streams there have High-grade bituminous sandstone______10 tain northwest of Santa Cruz, and west of the town River and Waddell and Pescadero creeks. This generally cut deep, narrow gullies in the recent Soft, pure white sandstone (thickness unknown). of Felton. This stone is extensively quarried and rainfall, combined with the dense fogs which are materials which clog their valleys, and appear Where exposed to the weather for a long time, as burned into lime and is the chief source of lime for common in the Big Basin region and in the region to have been recently rejuvenated. The recent on the outcropping edges of the bituminous rock in this part of the State. The stone could also be covered by the headwaters of the above-named movements along the coast line have been differ­ ravines, the rock turns first to a lead gray and utilized, in connection with clay or shale, for the streams, made possible the dense growth of redwoods ential, as is attested by the fact that the lowest finally to a much lighter color. manufacture of Portland cement, and a cement that formerly covered the whole of the central por­ sea terrace ranges in height from but a few feet The zone of the bituminous rock is exposed near plant is now in operation near Davenport Landing tion of the quadrangle. above tide to a hundred feet. Similar differences the base of the diatomaceous shale from Santa Cruz using clay from the Monterey to mix with the pure In the Santa Clara Valley the most important in elevation have been observed in other and northwestward as far as the western side of the Big limestone. water supply is that found in the gravel beds which higher terraces, especially in the region of San Basin, a distance of more than 20 miles. Through­ There are also many small limestone bodies in underlie practically the whole valley floor. Gregorio and Purisima. The axes of elevation of out this distance the dip of the lower part of the the Franciscan rocks on the east side of the Cahil- Flowing wells are obtained by penetrating these the lowest terrace correspond with old axes of diatomaceous shale and of the immediately under­ Castle Rock divide, but in these areas the limestone is gravels in the lower portion of the Santa Clara disturbance along the coast, and it is certain that lying sandstone is gently to the west and southwest. generally much less pure than that found in the plain, bordering the Bay of San Francisco. faulting and possibly folding are now going on in At many places through this district the sandstone vicinity of Santa Cruz. This rock is being quar­ Reservoirs have been constructed at several places the Santa Cruz Range, along some of the old lines beds are more or less bituminous but at only the one ried near the head of , where in the valley which follows the line of the San of weakness. locality mentioned above have they been found to several thousand tons^of crushed limestone are pro­ Andreas fault. These reservoirs collect a portion The uplift of the lower terraces, especially from be of commercial value. duced annually and shipped to beet-sugar factories. of the waters from the east side of Cahil and Castle Santa Cruz to the mouth of Waddell Creek, has Development work has been carried on at the Rock ridges. The most important are Crystal various quarries during a considerable period of DIATOMACEOUS SHALE. Springs and Searsville lakes. The former is at the been geologicallyO O v recent,' as is shown byv the narrow V-shaped canyons through which the streams in time, and much asphalt rock has been removed. Diatomaceous shale is found in great quantities north edge of the quadrangle and is used as a source that region invariably flow. Only those portions of the rock are saved which in the quadrangle, and could be used for polishing of supply for San Francisco. The latter collects the During and since the last coastal oscillations the contain a high percentage of asphalt, at least as powder, for packing steam pipes, and for filters. waters from the upper portion of the drainage basin Bay of San Francisco has been gradually silting high as is ordinarily used for paving. This Usually, however, it is too impure to compete with of San Francisquito Creek. A few small and up with debris brought in by the land streams. heavily charged rock is shipped and utilized directly the purer varieties which abound elsewhere. unimportant reservoirs for local use only have been The same streams are also building out alluvial for paving and other purposes. built elsewhere on the east side of the main water­ ' SAND. fans over the salt and brackish-water deposits shed. around the edge of the valley. These alluvial PETROLEUM. Much nearly pure sand is found at the base of The run-off from Stevens Creek and Campbell fans encroach upon the salt-water deposits at the Wells have been bored for oil at various places the Santa Margarita formation east of the town of Creek drainage basins is considerable during the bay shore and have covered the edges of the valley in the Santa Cruz quadrangle, but petroleum has Ben Lomond and in the region of Scott Valley. winter months, and these streams form a possible with recent stream deposits, which at some places been found in commercial quantities only in a lim­ Examination of this sand bed in detail might dis­ future source of water supply that may be of some have a thickness of 100 to 200 feet. The fresh­ ited area southeast of Purisima. Here small quan­ close portions of sufficient purity to be used in the importance. water gravel, sand, and clay become thinner and tities of a light oil of excellent quality are obtained manufacture of glass. April, 1908. Santa Cruz.