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Research about San Luis Obispo County, California

Source-linked reports with geographic coverage including San Luis Obispo County, California.

11 recordsLinked to original sources
USGS2015

Offshore geology and geomorphology from Point Piedras Blancas to Pismo Beach, San Luis Obispo County, California

Marine geology and geomorphology were mapped along the continental shelf and upper slope between Point Piedras Blancas and Pismo Beach, California. The map area is divided into the following three (smaller) map areas, listed from north to south: San Simeon, Morro Bay, and Point San Luis. Each smaller map area consists of a geologic map and the corresponding geophysical data that support the geologic mapping. Each geophysical data sheet includes shaded-relief multibeam bathymetry, seismic-reflection-survey tracklines, and residual magnetic anomalies, as well as a smaller version of the geologic map for reference. Offshore geologic units were delineated on the basis of integrated analysis of adjacent onshore geology, seafloor-sediment and rock samples, multibeam bathymetry and backscatter imagery, magnetic data, and high-resolution seismic-reflection profiles. Although the geologic maps are presented here at 1:35,000 scale, map interpretation was conducted at scales of between 1:6,000 and 1:12,000. Sea level was approximately 120 to 130 m lower during the Last Glacial Maximum (about 21 ka). This approximate depth corresponds to the modern shelf break, a lateral change from the gently dipping (0.8° to 1.0°) outer shelf to the slightly more steeply dipping (about 1.5° to 2.5°) upper slope in the central and northern parts of the map area. South of Point San Luis in San Luis Bay, deltaic deposits offshore of the mouth of the Santa Maria River (11 km south of the map area) have prograded across the shelf break and now form a continuous low-angle (about 0.8°) ramp that extends to water depths of more than 160 m. The shelf break defines the landward boundary of slope deposits. North of Estero Bay, the shelf break is characterized by a distinctly sharp slope break that is mapped as a landslide headscarp above landslide deposits. Multibeam imagery and seismic-reflection profiles across this part of the shelf break show evidence of slope failure, such as slumping, sliding, and soft-sediment deformation, along the entire length of the scarp. Notably, this shelf-break scarp corresponds to a west splay of the Hosgri Fault that dies out just north of the scarp, suggesting that faulting is controlling the location (and instability) of the shelf break in this area.

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USGS2001

Use of InSAR to identify land-surface displacements caused by aquifer-system compaction in the Paso Robles area, San Luis Obispo County, California, March to August 1997

The population in San Luis Obispo County has grown steadily during the 1990s, and some land use has been converted from dry farming to grazing to irrigated vineyards and urban areas. Because insufficient surface-water supplies are available to meet the growing demand, ground-water pumpage has increased and the resulting water-level declines have raised concern that this water resource may become overstressed. One particular concern is whether the larger ground-water basins within the county function as large individual basins or whether subsurface structures divide these large basins into smaller subbasins, as differences in ground-water-level data suggest. Interferometric Synthetic Aperture Radar (InSAR) is used in locating land-surface displacement, which may indicate subsurface structures in ground-water basins by determining seasonal and historical land-surface changes. Owing to the high spatial detail of InSAR imagery, the InSAR-derived displacement maps can be used with ground-water-level data to reveal differential aquifer-system compaction related to the presence of geological structures or the distribution of compressible sediments that may define subbasin boundaries. This report describes InSAR displacement maps of the Paso Robles area of San Luis Obispo County and compares them to maps of seasonal changes in ground-water levels to detect the presence of aquifer-system compaction.

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USGS2001

Use of InSAR to identify land-surface displacements caused by aquifer-system compaction in the Paso Robles area, San Luis Obispo County, California, March to August 1997

The population in San Luis Obispo County has grown steadily during the 1990s, and some land use has been converted from dry farming to grazing to irrigated vineyards and urban areas. Because insufficient surface-water supplies are available to meet the growing demand, ground-water pumpage has increased and the resulting water-level declines have raised concern that this water resource may become overstressed. One particular concern is whether the larger ground-water basins within the county function as large individual basins or whether subsurface structures divide these large basins into smaller subbasins, as differences in ground-water-level data suggest. Interferometric Synthetic Aperture Radar (InSAR) is used in locating land-surface displacement, which may indicate subsurface structures in ground-water basins by determining seasonal and historical land-surface changes. Owing to the high spatial detail of InSAR imagery, the InSAR-derived displacement maps can be used with ground-water-level data to reveal differential aquifer-system compaction related to the presence of geological structures or the distribution of compressible sediments that may define subbasin boundaries. This report describes InSAR displacement maps of the Paso Robles area of San Luis Obispo County and compares them to maps of seasonal changes in ground-water levels to detect the presence of aquifer-system compaction.

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USGS1999

Patch to landscape patterns in post fire recruitment of a serotinous conifer

Obligate seeding species are highly specialized to fire disturbance and many conifers such as cypress, which are adapted to high intensity stand-replacing fires, have canopy seed banks stored in serotinous cones. Resilience of these trees to fire disturbance is a function of disturbance frequency and one focus of this study was to determine the effect of patch age on postfire recruitment. A second focus was to determine the extent to which fire induced a landscape level change in the location of the forest boundary. Prior to a fire in 1994, a large Cupressus sargentii forest was a mosaic landscape of different aged patches of nearly pure cypress bordered by chaparral. Patches less than 60 years of age were relatively dense with roughly one tree every 1–2 m 2 but older patches had thinned to one tree every 3–15 m 2 . Older trees had substantially greater canopy cone crops but the stand level seed bank size was not significantly correlated with stand age. Fire-dependent obligate seeding species are sensitive to fire return interval because of potential changes in the size of seed banks – facing both a potential `immaturity risk' and a `senescence risk'. At our site, C. sargentii regeneration was substantial in stands as young as 20 years, suggesting that fire return interval would need to be shorter than this to pose any significant risk. Reduced seedling recruitment in stands nearly 100 years of age may indicate risk from senescence is greater, however, even the lowest density seedling recruitment was many times greater than the density of mature forests – thus this cypress would appear to be resilient to a wide range of fire return intervals. Changes in landscape patterning of forest and chaparral are unlikely except after fire. Factors that inhibit tree establishment within the shrubland, as well as factors that affect shrub establishment within the forest border likely affect the `permeability' of this ecotone. After the 1994 fire this boundary appeared to be stable in that cypress recruited best within the shadow of burned canopies and cypress were weak invaders of adjacent shrublands.

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USGS1988

Geologic map of the northwestern Caliente Range, San Luis Obispo County, California

The map area lies in the southern Coast Ranges of California, north of the Transverse Ranges and west of the southern San Joaquin Valley. This region is part of the Salinia-Tujunga composite terrane that is bounded on the northeast by the San Andreas fault (fig. 1) and on the southwest by the Nacimiento fault zone (Vedder and others, 1983). The Chimineas fault of this map is inferred to be the boundary between the Salinia and the Tujunga terranes (Ross, 1972; Vedder and others, 1983). Geologic mapping in the region of the California Coast Ranges that includes the area of this map has been largely the work of T.W. Dibblee, Jr. Compilations of geologic mapping at a scale of 1:125,000 (Dibblee, 1962, 1973a) provide the regional setting for this map, the northeast border of which lies about 6 to 7 km southwest of the San Andreas fault. Ross (1972) mapped the crystalline basement rocks in the vicinity of Barrett Creek, along the northeast side of the Chimineas fault ("Barrett Ridge" of Ross, 1972). Recent 1:24,000-scale mapping in the La Panza Range (fig. 1) (Vedder and others 1986a,b) overlaps onto the southwest edge of this map and provides useful information about the older rocks, mostly southwest of San Juan Creek. Stratigraphic knowledge of the area, which lies in the northern part of the middle Tertiary Cuyama basin, has evolved over a period of years beginning with the molluscan biostratigraphic work of Anderson and Martin (1914) and Loel and Corey (1932). Hill and others (1958) described the Tertiary stratigraphy of the region and proposed stratigraphic names. This stratigraphy was discussed further by Dibblee (1973b), and his revised nomenclature is used here. Stratigraphic studies in the southeastern Caliente Range (fig. 1) (Repenning and Vedder, 1961; Vedder, 1973) provided valuable information on the interrelations of continental, shallow-marine, and deeper marine facies in the southern part of the Cuyama basin, which have basinwide application. More recent stratigraphic studies by Lagoe (1984, 1985, 1987, 1988) further elaborate on aspects of Miocene basin history and paleogeography. Contributions to the tectonic history of the area have been made by Schwade and others (1958), on the basis of oil exploration in the Cuyama Valley area (fig. 1) in the 1940's and 1950's; by Bartow (1974), as part of a regional stratigraphic study; by Ballance and others (1983), on the basis of a study of Oligocene and early Miocene sedimentation; and most recently by Davis and others (1988) and Yeats and others (1988), who utilized a variety of new data from seismic reflection and from stratigraphic and structural studies. Field work for this map was done mostly in 1969-73 as part of a regional study of the Simmler and Vaqueros Formations (Bartow, 1974). Detailed field mapping was, therefore, concentrated on those units; other parts of the area were mapped by geologic reconnaissance and air-photo interpretation that were supplemented by data from published maps (Dibblee, 1973a; Vedder and others, 1986a,h). Mapping of the crystalline basement rocks at "Barrett Ridge" is from Ross (1972, plate 1). The structural style depicted in the accompanying cross sections favors the thrust belt concepts of Davis and others (1988) over the older interpretations of Dibblee (1962) or Cross (1962).

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USGS1976

Sediment discharge in the Upper Arroyo Grande and Santa Rita Creek basins, San Luis Obispo County, California

Sediment data collected in the upper Arroyo Grande and Santa Rita Creek basins, San Luis Obispo County, California, during the 1968-73 water years were analyzed to determine total sediment discharge at four stations in the basins. Water discharge and total sediment discharge at these stations, representative of the 1943-72 period, were estimated from long-term flow data for nearby gaging stations and water-sediment discharge relations determined for the 1968-73 water years. Most of the total annual sediment discharge at each station occurs during a few days each year. The quantity of sediment transported in a single day often accounts for more than 40 percent of the total annual sediment discharge. Estimated sediment discharge for the upper Arroyo Grande and Santa Rita Creek basins during the 1943-72 water years averaged 53,000 tons and 23,000 tons per year. Long-term sediment deposition in Lopez Reservoir, which is in the southern part of the upper Arroyo Grande basin, was estimated to be 35 acre-feet per year. (Woodard-USGS)

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