We have studied detrital-zircon U-Pb age spectra and conglomerate clast populations from Neogene-Quaternary siliciclastic and volcaniclastic strata of the southeastern San Joaquin Basin, as well as a fault-controlled Neogene basin that formed across the southernmost Sierra Nevada; we call this basin the Walker graben. The age spectra of the detrital-zircon populations are compared to a large basement zircon age data set that is organized into age populations based on major drainage basin geometry of the southern Sierra Nevada and adjacent ranges. We find a direct sediment provenance and dispersal link for much of the Neogene between the Walker graben and the southeastern San Joaquin Basin. In early to middle Miocene time, this link was accented by the delivery of volcaniclastic materials into the southeastern Basin margin from the Cache Peak volcanic center that was nested within the Walker graben. In late middle Miocene through early Pleistocene time, this linkage was maintained by a major fluvial system that we call the Caliente River, whose lower trunk was structurally controlled by growth faults along the Edison graben, which breached the western wall of the Walker graben. The Caliente River redistributed into the southeastern San Joaquin Basin much of the ~2 km of volcaniclastic and siliciclastic strata that filled the Walker graben. This sediment redistribution was forced by a regional topographic gradient that developed in response to uplift along the eastern Sierra escarpment system. The Caliente River built a fluvial-deltaic fan system that prograded northwestward across the lower trunk of the Kern River and thereby deflected the Kern drainage flux of sediment into the Basin edge northward. In mainly late Miocene time, turbidites generated primarily off the Caliente River delta front built the Stevens submarine fan system of the southeastern and central areas of the San Joaquin Basin. In late Quaternary time, 1-1.8 km of Caliente River-built strata were eroded as an epeirogenic uplift that we call the Kern arch emerged along the southeastern Basin margin, in response to underlying mantle lithosphere removal. The sediment that was eroded off the arch was redistributed mainly into the Maricopa and Tulare sub-basins that are located to the southwest and northwest, respectively, of the arch.

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Water salinity in the San Joaquin Valley is a function of depth, location, and stratigraphy. This paper presents a reconnaissance study of water salinity within Kern County, California, using chemical analyses from oil field produced water and water wells as well as geophysical logs. Log analysis indicates that the base of underground sources of drinking water (USDWs) (<10,000 mg/L) slopes from northwest to southeast. Lab analyses show that USDWs extend to depths as great as 1900 m (6233.5 ft) southeast of Bakersfield. This area receives the greatest amount of fresh water recharge from streams flowing westward from the Sierras. The marine Olcese Sand is more saline than the overlying and underlying aquifers and separates the aquifers into an upper and lower USDW. Log analysis also indicates a zone of higher salinity separating zones of lower salinity in this area. Salinities in the west are higher, and depths to base USDW are variable. Although waters in many sands in the western valley are more saline than 3000 ppm total dissolved solids (TDS), numerous wells contain waters between 3000 and 10,000 ppm at depths of less than 600 m (1968.5 ft), particularly in the nonmarine Tulare Formation. At North Belridge field, a salinity reversal is apparent below 2100 m (6890 ft). Waters above this depth are approximately 40,000 mg/L TDS, whereas water salinities below 2200 m (7218 ft) range from 10,000 to 32,000 mg/L. Extremely high salinities are found in several wells less than 30 m (98 ft) deep, primarily in the northwestern area. These may be perched aquifers or lie adjacent to unmapped agricultural drainage sumps and do not reflect salinities in the regional aquifer.

Enhanced oil recovery (EOR) and hydraulic fracturing practices are commonly used methods to improve hydrocarbon extraction efficiency; however, the environmental effects of such practices remain poorly understood. EOR is particularly prevalent in oil fields throughout California where water resources are in high demand and the disposal of large volumes of produced water may affect groundwater quality. Consequently, it is essential to better understand the fate of injected (EOR) fluids in California, and other subsurface petroleum systems, as well as any potential effect on nearby aquifer 2 systems. Noble gases can be used as tracers to understand hydrocarbon generation, migration, and storage conditions, as well as the relative proportions of oil and water present in the subsurface. In addition, a noble gas signature diagnostic of injected (EOR) fluids can be readily identified. We report noble gas isotope and concentration data in casing gases from oil production wells in the Lost Hills oil field, northwest of Bakersfield, California, and injectate gas data from the Fruitvale oil field, located within the city of Bakersfield. Casing and injectate gas data are used to: 1) establish pristine hydrocarbon noble-gas signatures and the processes controlling noble gas distributions, 2) characterize the noble gas signature of injectate fluids, 3) trace injectate fluids in the subsurface, and 4) construct a model to estimate EOR efficiency. Noble gas results range from pristine to significantly modified by EOR, and can be best explained using a solubility exchange model between oil and connate/formation fluids, followed by gas exsolution upon production. This model is sensitive to oil-water interaction during hydrocarbon expulsion, migration, and storage at reservoir conditions, as well as any subsequent modification by EOR.

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