Geology and geomorphology--Offshore of Aptos Map Area, California

This part of DS 781 presents data for the geologic and geomorphic map of the Offshore Aptos map area, California. The vector data file is included in "Geology_OffshoreAptos.zip," which is accessible from http://dx.doi.org/10.5066/F7K35RQB. Most of the offshore occupies very gently dipping (about 0.1° to 0.4°) continental shelf, extending from the nearshore to water depths of about 70 m. In the southwestern part of the map, the shelf is incised by the north-trending head of Soquel Canyon, which has a maximum depth of 260 m on the south edge of the map. The shelf is underlain by late Neogene bedrock and a variably thick (as much as 32 m) late Quaternary sediment cover. Sea level has risen 120 to 130 m over about the last 21,000 years (for example, Stanford and others, 2011), leading to broadening of the continental shelf, progressive eastward migration of the shoreline and wave-cut platform, and transgressive erosion and deposition. Sea-level rise was apparently not steady during this period, leading to development of shoreline angles and adjacent submerged wave-cut platforms and risers (Kern, 1977). These features commonly are commonly removed by erosion or buried by shelf sediment, however their original morphology is at least partly preserved along the rim of upper Soquel Canyon. Geologic map units include three wave-cut platforms (units Qwp1, Qwp2, Qwp3) and risers (units Qwpr1, Qwpr2, Qwpr3), separated by shoreline angles at depths of approximately 96 to 100 m, 108 m, and 120 to 125 m. The deepest paleoshoreline (about 120 m deep) approximately corresponds to sea level during the final stages of the last sea-level lowstand (Stanford and others, 2011). Submergence during sea-level rise also cut off the direct connection between Soquel Canyon and coastal watersheds, rendering the submarine canyon relatively inactive. Although slightly sheltered in Monterey Bay, the Offshore of Aptos map area is now subjected to significant wave energy and strong currents. Shelf morphology and geology are also affected by local faulting, folding, and uplift. The shelf in the Offshore of Aptos map area is cut by a diffuse zone of northwest-striking, steeply dipping to vertical faults mapped with high-resolution, seismic-reflection profiles. Faults are mapped on the basis of abrupt truncation or warping of reflections and (or) juxtaposition of reflection panels with different seismic parameters. Seismic profiles traversing this diffuse zone cross as many as 13 faults over a distance of 8 km. Mapped fault lengths in this diffuse zone are typically 2 to 7 km, and the strike of these offshore faults rotates from about 325° to 350° from southwest to northeast. Faults in this diffuse zone cut through Neogene bedrock and locally appear to disrupt overlying latest Quaternary sediments, and the presence of warped reflections along some fault strands suggests there may be both vertical and strike-slip offsets. This broad, distributed zone of deformation resembles the northwest-trending Monterey Bay Fault Zone (Greene, 1977, 1990), which occurs about 10 km farther west in outer Monterey Bay and similarly lacks a lengthy continuous "master fault." Deformation in both the Monterey Bay Fault zone and the diffuse zone of faults in the Offshore of Aptos map area is attributable to its location in the 40-km-wide, northward-narrowing structural zone between two major, right-lateral, strike-slip faults, the San Andreas Fault to the east and the offshore San Gregorio Fault to the west (McCulloch, 1987; Brabb, 1997; Wagner and others, 2002; Dickinson and others, 2005). Emergent late Pleistocene marine terraces on the south flank of the Santa Cruz Mountains in and north of northeastern Monterey Bay are as high as 125 m. Anderson and Menking (1994) report a 50- to 60-m elevation for the shoreline angle tied to the lowest emergent terrace (assigned to oxygen isotope stage 5c or 5e) in the Aptos vicinity, suggesting an uplift rate of about 0.4 to 0.6 mm/yr. Anderson (1990) and Anderson and Menking (1994) attributed this uplift to advection of crust around a bend in the San Andreas Fault, which lies 13 km northeast of the Aptos shoreline. The uplifted region in this tectonic model would include the nearshore and shelf of northeastern Monterey Bay, but there are considerable shore-normal uplift gradients and offshore uplift rates are not constrained. From La Selva Beach west to the western edge of the map area, the upper Miocene and Pliocene Purisima Formation (unit Tp; Powell and others, 2007) forms discontinuous outcrops that extend from coastal bluffs into the offshore to depths as great as 25 m. The seafloor outcrops are most prominent offshore of Soquel Point and have relatively low relief, probably in large part due to low structural dips. The Purisima Formation also forms outcrops in the steep walls of the head of Soquel Canyon. Other "hard bottom" in the map area is mapped at the location of a wastewater outfall pipe offshore of the mouth of the Pajaro River (artificial fill; unit af). Modern nearshore and inner- to mid-shelf sediments are mostly sand (unit Qms) and a mix of sand and gravel (units Qmsc and Qmsd). There is an extensive area in northeastern Monterey Bay where unit Tp bedrock is overlain a very thin cover of Qms; such areas are mapped and labeled as composite units (Qms/Tp) and shown with a stippled pattern on the map. Storlazzi and others (2011) showed that active sediment transport in the nearshore of northern Monterey Bay can lead to significant burial and exhumation of offshore bedrock reefs, and it is likely that the sediment cover in the mapped composite areas is ephemeral and transient. The more coarse-grained sands and gravels (units Qmsc and Qmsd) are primarily recognized on the basis of bathymetry and high backscatter. Unit Qmsc occurs only adjacent to bedrock at Soquel Point in water depths less than 20 m. Unit Qmsd forms erosional lags in scoured depressions at water depths ranging from about 10 to 25 m. The Qmsd depressions have irregular to lenticular outlines; are a few tens of centimeters deep; range in size from a few 10's to as much as about 54,000 m2; and are either bounded by relatively sharp and less commonly diffuse contacts with unit Qms sands, or by abrupt contacts with seafloor bedrock outcrops. Qmsd depressions are most abundant in a northeast-trending zone between Seacliff State Beach and La Selva Beach, where they form distinct, narrow (< 50 m) linear, bands that extend about 4 km offshore. Scour depressions similar to those mapped adjacent to bedrock near Soquel Point are common along this stretch of the California coast (see, for example, Hallenbeck and others, 2012; Davis and others, 2013). Such features have been referred to as "rippled-scour depressions" (see, for example, Cacchione and others, 1984) or "sorted bedforms" (see, for example, Goff and others, 2005; Trembanis and Hume, 2011). They form where surficial offshore sandy sediment is relatively thin (thus unable to fill the depressions) due to both low sediment supply and to erosion and transport of sediment during large ocean swells. The elongate, linear, shore-normal bands of scour depressions between Aptos and La Selva Beach are morphologically anomalous; this mode of occurrence has not been recognized elsewhere along the California coast. Although the general areas in which both unit Qmsd scour depressions and surrounding Qms sand sheets occur are not likely to change substantially, the boundaries of the unit(s) are likely ephemeral, changing seasonally and during significant storm events. An offshore transition from unit Qms to the more fine-grained marine sediments of unit Qmsf occurs at water depths of 25 to 30 m. Unit Qmsf is commonly extensively bioturbated and consists primarily of mud and muddy sand. Edwards (2002) and Grossman and others (2006) suggested these fine-grained sediments form an extensive "mid-shelf mud belt" that was primarily sourced by the San Lorenzo River, Pajaro River, and smaller coastal watersheds. A 4.3 km2 zone of hummocky seafloor (Qmsh) surrounded by fine-grained Qmsf occurs in the southeastern part of the map area at 30 to 35 m water depth, about 3 to 4 km north of the head of Soquel Canyon. Bathymetric contours reveal that the hummocky zone has an embayed up-slope margin, and relief on hummocks within the zone is as much as 100 cm over 100 m. The hummocky zone probably formed by liquefaction, and associated induced ground failure forced by strong ground motions from earthquakes. The embayed upper margin of the zone also indicates some slumping, surprising given the extremely gentle dip of the shelf (about 0.2°) at this location. Earthquake sources for strong ground motions could include the distributed fault zone in northeastern Monterey Bay (several mapped faults cut the hummocky area) or the nearby San Andreas Fault (20 km to the northeast) or San Gregorio Fault (19 km to the southwest). Recent large earthquakes on the San Andreas Fault include the M 6.9 1989 Loma Prieta earthquake and the M 7.8 1906 Great California earthquake (Northern California Earthquake Data Center, 2014). Soquel Canyon is a tributary to the much larger Monterey Canyon system (Greene and others, 2002). The canyon axis plunges south about 4°; side-canyon walls generally dip about 5° but are locally as steep as 20° to 25°. Non-bedrock geologic units in Soquel Canyon are largely defined and delineated on the basis of geomorphology. Unit Qcw represents mud and sand draped over the upper submarine canyon wall. Unit Qcfa represents the mainly mud fill of the inactive axial canyon channel. References Cited Anderson, R.S., 1990, Evolution of the northern Santa Cruz Mountains by advection of crust past a San Andreas Fault bend: Science, v. 249, p. 397-401. Anderson, R.S., and Menking, K.M., 1994, The Quaternary marine terraces of Santa Cruz, California-Evidence for coseismic uplift on two faults: Geological Society of America Bulletin, v. 106, p. 649-664. Brabb, E.E., 1997, Geologic Map of Santa Cruz County, California: A digital database, US Geological Survey Open-File Report 97-489, 1:62,500. Davis, A.C.D., Kvitek, R.G., Mueller, C.B.A., Young, M.A., Storlazzi, C.D., and Phillips, E.L., 2013, Distribution and abundance of rippled scour depressions along the California coast: Continental Shelf Research, v. 69, p. 88-100. Dickinson, W.R., Ducea, M., Rosenberg, L.I., Greene, H.G., Graham, S.A., Clark, J.C., Weber, G.E., Kidder, S., Ernst, W.G., and Brabb, E.E., 2005, Net dextral slip, Neogene San Gregorio-Hosgri Fault Zone, coastal California: Geologic evidence and tectonic implications: Geological Society of America Special Paper 391, 43 p. Edwards, B.D., 2002, Variations in sediment texture on the northern Monterey Bay National Marine Sanctuary continental shelf: Marine Geology, v. 181, p. 83-100. Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms or "rippled scour depressions", within the Martha’s Vineyard Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461-484. Greene, H.G., 1977, Geology of the Monterey Bay region: U.S. Geological Survey Open-File Report 77-718, 347 p. Greene, H.G., 1990, Regional tectonics and structural evolution of the Monterey Bay region, central California, in Garrison, R.E., Greene, H.G., Hicks, K.R., Weber, G.E., and Wright, T.L., eds., Geology and tectonics of the central California coastal region, San Francisco to Monterey, Pacific Section American Association of Petroleum Geologists, Guidebook GB-67, p. 31-56. Greene, H.G., Maher, N.M., and Paull, C.K., 2002, Physiography of the Monterey Bay National Marine Sanctuary and implications about continental margin development: Marine Geology, v. 181, p. 55-82. Grossman, E.E., Eittreim, S.L., Field, M.E., and Wong, F.L., 2006, Shallow stratigraphy and sedimentation history during high-frequency sea-level changes on the central California shelf: Continental Shelf Research, v. 26, p1217-1239. Hallenbeck, T.R., Kvitek, R.G., and Lindholm, J., 2012, Rippled scour depressions add ecologically significant heterogeneity to soft-bottom habitats on the continental shelf: Marine Ecology Progress Series, v. 468, p. 119-133. Kern, J.P., 1977, Origin and history of upper Pleistocene marine terraces, San Diego, California: Geological Society of America Bulletin, v. 88, p. 1,553-1,566. McCulloch, D.S., 1987, Regional geology and hydrocarbon potential of offshore central California, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology and Resource Potential of the Continental Margin of Western North America and Adjacent Oceans -- Beaufort Sea to Baja California: Houston, Texas, Circum-Pacific Council for Energy and Mineral Resources, Earth Science Series, v. 6., p. 353-401. Northern California Earthquake Data Center, 2014, Northern California earthquake catalog: Northern California Earthquake Data Center database, accessed April 5, 2014, at http://www.ncedc.org/ncsn/. Powell, Charles L., II, Barron, John A., Sarna-Wojcicki, Andrei M., Clark, Joseph C., Perry, Frank A., Brabb, Earl E., and Fleck, Robert J., 2007, Age, stratigraphy, and correlations of the late Neogene Purisima Formation, central California Coast Ranges: U.S. Geological Survey Professional Paper 1740, 32 p., available at http://pubs.usgs.gov/pp/2007/1740/. Stanford, J.D., Hemingway, R., Rohling, E.J., Challenor, P.G., Medina-Elizalde, M., and Lester, A.J., 2011, Sea-level probability for the last deglaciation, statistical analysis of far-field records: Global and Planetary Change, v. 79, p. 193-203. Storlazzi, C.D., Fregoso, T.A., Golden, N.E., and Finlayson, D.P., 2011, Sediment dynamics and the burial and exhumation of bedrock reefs along an emergent coastline as elucidated by repetitive sonar surveys-northern Monterey Bay, CA: Marine Geology, v. 289, p. 46-59. Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand-Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203-214. Wagner, D.L., Greene, H.G., Saucedo, G.J., and Pridmore, C.L., 2002, Geologic Map of the Monterey 30' x 60' quadrangle and adjacent areas, California: California Geological Survey Regional Geologic Map Series, scale 1:100,000.本数据集DS 781的此部分提供了加利福尼亚州阿普托斯（Aptos）近海制图区的地质与地貌图数据。矢量数据文件包含于"Geology_OffshoreAptos.zip"中，可通过http://dx.doi.org/10.5066/F7K35RQB获取。 该区域大部分近海区域为坡度极缓（约0.1°至0.4°）的大陆架（continental shelf），范围从近岸延伸至约70米水深处。在制图区西南部，大陆架被北走向的索克尔峡谷（Soquel Canyon）头部切割，该峡谷在制图区南缘的最大水深达260米。大陆架基底为新近纪（Neogene）晚期基岩，以及厚度不均（最大可达32米）的晚第四纪（late Quaternary）沉积盖层。 过去约21000年间，海平面上升了120至130米（Stanford等，2011），导致大陆架拓宽、海岸线与浪蚀台地（wave-cut platform）逐步向东迁移，同时发生海侵侵蚀与沉积作用。此期间海平面上升并非匀速，进而形成了海岸线角以及邻近的淹没浪蚀台地和阶地陡坎（Kern，1977）。这些地貌通常会被侵蚀作用破坏或被大陆架沉积物掩埋，但在上索克尔峡谷的边缘地带，其原始形态至少得到了部分保留。 地质图图例包含三个浪蚀台地（单元Qwp1、Qwp2、Qwp3）和阶地陡坎（单元Qwpr1、Qwpr2、Qwpr3），它们被不同水深的海岸线角分隔，对应水深分别约为96至100米、108米以及120至125米。最深的古海岸线（约120米水深）大致对应末次海平面低水位期（sea-level lowstand）最终阶段的海平面高度（Stanford等，2011）。海平面上升过程中的淹没作用还切断了索克尔峡谷与沿海流域的直接连通，使得该海底峡谷相对不活跃。尽管阿普托斯近海制图区在蒙特雷湾（Monterey Bay）内略有遮蔽，但目前仍承受着显著的波浪能量和强劲的海流作用。 大陆架的形态与地质特征还受到局部断裂作用、褶皱作用和抬升作用的影响。阿普托斯近海制图区的大陆架被一个走向北西、倾角陡峭至直立的弥散断裂带切割，该断裂带通过高分辨率地震反射剖面进行填图。断裂的识别依据为反射层的突然截断或弯曲，以及（或）具有不同地震参数的反射段的并置。穿过该弥散断裂带的地震剖面在8公里范围内可识别出多达13条断层。该弥散断裂带内的已填图断层长度通常为2至7公里，且这些近海断层的走向从西南到东北从约325°旋转至350°。该弥散断裂带内的断层切穿新近纪晚期基岩，局部似乎扰乱了上覆的晚第四纪沉积物；部分断层段沿线存在弯曲的反射层，表明其可能兼具垂直位移和走滑位移（strike-slip offsets）。这一宽阔的弥散变形带与北西走向的蒙特雷湾断裂带（Monterey Bay Fault Zone，Greene，1977、1990）相似，后者位于蒙特雷湾外海约10公里处，同样缺乏一条长距离连续的“主控断层”。 蒙特雷湾断裂带和阿普托斯近海制图区的弥散断裂带的变形作用，均可归因于其所处的构造位置：该区域位于两条大型右旋走滑断层之间宽40公里、向北收窄的构造带内，东侧为圣安德烈亚斯断层（San Andreas Fault），西侧为近海的圣格雷戈里奥断层（San Gregorio Fault，McCulloch，1987；Brabb，1997；Wagner等，2002；Dickinson等，2005）。 蒙特雷湾东北部及以北区域圣克鲁斯山脉（Santa Cruz Mountains）南翼出露的晚更新世（late Pleistocene）海成阶地，海拔最高可达125米。Anderson和Menking（1994）报道，阿普托斯附近与最低出露海成阶地（对应氧同位素阶段5c或5e）相关的海岸线角海拔为50至60米，据此推算抬升速率约为0.4至0.6毫米/年。Anderson（1990）以及Anderson和Menking（1994）将该抬升作用归因于圣安德烈亚斯断层拐弯处的地壳平流作用，该断层位于阿普托斯海岸线东北方向13公里处。该构造模型中的抬升区域应包括蒙特雷湾东北部的近岸与大陆架，但存在显著的垂直海岸线抬升梯度，且近海抬升速率尚未得到约束。 从拉塞尔瓦海滩（La Selva Beach）向西至制图区西缘，上中新统（upper Miocene）和上新统（Pliocene）的普里西马组（Purisima Formation，单元Tp；Powell等，2007）形成不连续露头，从海岸悬崖延伸至近海，最大水深可达25米。海底露头在索克尔角（Soquel Point）近海最为显著，地形起伏相对较小，这可能在很大程度上源于构造倾角较低。普里西马组还在索克尔峡谷头部的陡峭岩壁中形成露头。制图区内的其他“硬质底”位于帕哈罗河（Pajaro River）河口近海的排污管道位置（人工堆积物，单元af）。 现代近岸及内-中陆架沉积物以砂（单元Qms）以及砂与砾石的混合物（单元Qmsc和Qmsd）为主。在蒙特雷湾东北部存在大片区域，其中单元Tp基岩上覆有极薄的Qms盖层；此类区域被填图为复合单元（Qms/Tp），并在图上以点纹图案表示。Storlazzi等（2011）的研究表明，蒙特雷湾北部近岸的活跃沉积物搬运作用可导致海底基岩礁体发生显著的掩埋与出露，因此上述复合单元所在区域的沉积物盖层可能是短暂且易变的。 粒度更粗的砂和砾石（单元Qmsc和Qmsd）主要通过水深测量和高反向散射数据识别。单元Qmsc仅分布于索克尔角附近水深小于20米的基岩区域。单元Qmsd形成于冲刷洼地中的侵蚀残留沉积，水深范围约为10至25米。Qmsd洼地轮廓不规则至透镜状，深度约为数十厘米，面积从数十平方米至最大约54000平方米不等，其边界要么与Qms砂层以相对清晰（少数情况为弥散）的接触带分界，要么与海底基岩露头以突变接触带分界。Qmsd洼地在西克利夫州立海滩（Seacliff State Beach）至拉塞尔瓦海滩之间的北西走向带内最为发育，形成狭窄（<50米）的线性条带，向海延伸约4公里。 与索克尔角附近基岩周边填绘的冲刷洼地相似的地貌，在加利福尼亚州海岸的该段区域十分常见（例如Hallenbeck等，2012；Davis等，2013）。此类地貌被称为“波纹冲刷洼地”（rippled-scour depressions，例如Cacchione等，1984）或“分选床形”（sorted bedforms，例如Goff等，2005；Trembanis和Hume，2011）。它们形成于表层离岸砂质沉积物较薄的区域——由于沉积物供给不足以及大型海洋涌浪引发的侵蚀和搬运作用，导致沉积物无法填满洼地。阿普托斯至拉塞尔瓦海滩之间的线性、垂直海岸线的冲刷洼地条带在形态上较为异常，这种产出模式在加利福尼亚州海岸其他区域尚未被发现。尽管Qmsd冲刷洼地和周边Qms砂层分布的大致区域不太可能发生显著变化，但该单元的边界可能是短暂的，会随季节和重大风暴事件发生变化。 在水深25至30米处，从Qms单元向更细粒的Qmsf单元海相沉积物发生近海相变。Qmsf单元通常发育强烈的生物扰动构造，主要由泥质和泥质砂组成。Edwards（2002）和Grossman等（2006）认为，这些细粒沉积物形成了广泛的“中陆架泥质带”，其物源主要为圣洛伦索河、帕哈罗河以及小型沿海流域。 在制图区东南部索克尔峡谷头部以北约3至4公里、水深30至35米处，存在一片面积4.3平方公里的丘状海底（Qmsh），周围被细粒的Qmsf沉积物环绕。水深测量等值线显示，该丘状带的上坡边缘呈海湾状，区内丘体的地形起伏在100米范围内可达100厘米。该丘状带可能由液化作用形成，相关的诱发地面破坏由地震强地面运动引发。该带的海湾状上缘还显示存在滑坡现象，考虑到该区域大陆架坡度仅约0.2°，这一点颇为出人意料。引发强地面运动的地震震源可能包括蒙特雷湾东北部的弥散断裂带（多条已填图断层穿过该丘状区域）、附近的圣安德烈亚斯断层（东北方向20公里处）或圣格雷戈里奥断层（西南方向19公里处）。圣安德烈亚斯断层上近期发生的大型地震包括1989年M 6.9的洛马普里塔地震和1906年M 7.8的加州大地震（北加州地震数据中心，2014）。 索克尔峡谷是更大规模的蒙特雷峡谷系统的支流（Greene等，2002）。峡谷轴线向南俯冲约4°；峡谷侧壁的坡度通常约为5°，但局部可达20°至25°。索克尔峡谷内的非基岩地质单元主要通过地貌特征进行圈定和填绘。单元Qcw代表覆盖在海底峡谷上部岩壁上的泥质和砂质沉积物。单元Qcfa代表不活动的峡谷轴向水道内的主要泥质充填物。 ### 参考文献 Anderson, R.S., 1990, Evolution of the northern Santa Cruz Mountains by advection of crust past a San Andreas Fault bend: Science, v. 249, p. 397-401. Anderson, R.S., and Menking, K.M., 1994, The Quaternary marine terraces of Santa Cruz, California-Evidence for coseismic uplift on two faults: Geological Society of America Bulletin, v. 106, p. 649-664. Brabb, E.E., 1997, Geologic Map of Santa Cruz County, California: A digital database, US Geological Survey Open-File Report 97-489, 1:62,500. Davis, A.C.D., Kvitek, R.G., Mueller, C.B.A., Young, M.A., Storlazzi, C.D., and Phillips, E.L., 2013, Distribution and abundance of rippled scour depressions along the California coast: Continental Shelf Research, v. 69, p. 88-100. Dickinson, W.R., Ducea, M., Rosenberg, L.I., Greene, H.G., Graham, S.A., Clark, J.C., Weber, G.E., Kidder, S., Ernst, W.G., and Brabb, E.E., 2005, Net dextral slip, Neogene San Gregorio-Hosgri Fault Zone, coastal California: Geologic evidence and tectonic implications: Geological Society of America Special Paper 391, 43 p. Edwards, B.D., 2002, Variations in sediment texture on the northern Monterey Bay National Marine Sanctuary continental shelf: Marine Geology, v. 181, p. 83-100. Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms or "rippled scour depressions", within the Martha’s Vineyard Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461-484. Greene, H.G., 1977, Geology of the Monterey Bay region: U.S. Geological Survey Open-File Report 77-718, 347 p. Greene, H.G., 1990, Regional tectonics and structural evolution of the Monterey Bay region, central California, in Garrison, R.E., Greene, H.G., Hicks, K.R., Weber, G.E., and Wright, T.L., eds., Geology and tectonics of the central California coastal region, San Francisco to Monterey, Pacific Section American Association of Petroleum Geologists, Guidebook GB-67, p. 31-56. Greene, H.G., Maher, N.M., and Paull, C.K., 2002, Physiography of the Monterey Bay National Marine Sanctuary and implications about continental margin development: Marine Geology, v. 181, p. 55-82. Grossman, E.E., Eittreim, S.L., Field, M.E., and Wong, F.L., 2006, Shallow stratigraphy and sedimentation history during high-frequency sea-level changes on the central California shelf: Continental Shelf Research, v. 26, p1217-1239. Hallenbeck, T.R., Kvitek, R.G., and Lindholm, J., 2012, Rippled scour depressions add ecologically significant heterogeneity to soft-bottom habitats on the continental shelf: Marine Ecology Progress Series, v. 468, p. 119-133. Kern, J.P., 1977, Origin and history of upper Pleistocene marine terraces, San Diego, California: Geological Society of America Bulletin, v. 88, p. 1,553-1,566. McCulloch, D.S., 1987, Regional geology and hydrocarbon potential of offshore central California, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology and Resource Potential of the Continental Margin of Western North America and Adjacent Oceans -- Beaufort Sea to Baja California: Houston, Texas, Circum-Pacific Council for Energy and Mineral Resources, Earth Science Series, v. 6., p. 353-401. Northern California Earthquake Data Center, 2014, Northern California earthquake catalog: Northern California Earthquake Data Center database, accessed April 5, 2014, at http://www.ncedc.org/ncsn/. Powell, Charles L., II, Barron, John A., Sarna-Wojcicki, Andrei M., Clark, Joseph C., Perry, Frank A., Brabb, Earl E., and Fleck, Robert J., 2007, Age, stratigraphy, and correlations of the late Neogene Purisima Formation, central California Coast Ranges: U.S. Geological Survey Professional Paper 1740, 32 p., available at http://pubs.usgs.gov/pp/2007/1740/. Stanford, J.D., Hemingway, R., Rohling, E.J., Challenor, P.G., Medina-Elizalde, M., and Lester, A.J., 2011, Sea-level probability for the last deglaciation, statistical analysis of far-field records: Global and Planetary Change, v. 79, p. 193-203. Storlazzi, C.D., Fregoso, T.A., Golden, N.E., and Finlayson, D.P., 2011, Sediment dynamics and the burial and exhumation of bedrock reefs along an emergent coastline as elucidated by repetitive sonar surveys-northern Monterey Bay, CA: Marine Geology, v. 289, p. 46-59. Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand-Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203-214. Wagner, D.L., Greene, H.G., Saucedo, G.J., and Pridmore, C.L., 2002, Geologic Map of the Monterey 30' x 60' quadrangle and adjacent areas, California: California Geological Survey Regional Geologic Map Series, scale 1:100,000.