ABSTRACT The prospective Sacramento Basin consists of approximately 4.6 million acres of Cretaceous-Tertiary area bounded on the west by the Sierra Nevada and on the east by the uplifted Coast Range terranes. The south margin extends to the Stockton Arch and the north productive limit lies near Red Bluff where Forbes objective section becomes diminished. Cretaceous objective section is dominated in the north by Forbes-Kione strata and in the south by the younger Starkey-Winters and equivalent strata. Overall the Sacramento basin is a south plunging trough containing over 40,000 feet of sediments in the Montezuma depocenter and interrupted by major structural features including the Rio Vista-Thornton Arch, transtensional Midland fault system, Sutter Tertiary Volcanics and transpressional Willows fault system. Productive zones range from about 2000 to 11,000 foot drill depths. With nearly 9500 wells drilled and about 3000 completed, the estimated ultimate recovery is nearly 10 trillion cubic feet (TCF) with an implied 14 TCF gas-in-place at 70% recovery. Ultimate recovery can be estimated by formation with nearly 40% from Tertiary rocks including 3.5 TCF from the Rio Vista field, 25% from the Cretaceous Forbes-Kione depositional system, and 35%from the Cretaceous Starkey-Winters depositional system. Severe overpressured marine Forbes strata in the North (Grimes-Sutter) area is largely due to tectonic uplift. Slight overpressure in marine Winters objectives at 11,000 feet is noted on the flanks of the Montezuma depocenter near Rio Vista. Both Forbes and Winters formation overpressure are capped in large part by thick slope shale sequences. Overlying Kione and Starkey deltaic fades and all Tertiary reservoirs are normally pressured. Present-day temperature gradients are extremely low, averaging 1.2 degrees F/100 ft. Vitrinite reflectance and source rock data suggest lean source rocks and low temperature gradients in most producing areas of the basin. With nearly all gas thermogenic in origin an implicit assumption obtains that an early oil phase was insufficient to saturate and allow significant expulsion. A later gas phase migrated from the deeper parts of the basin, particularly the Montezuma depocenter area and perhaps deeply buried Forbes source rock in the Grimes area, in general from below 12,000 feet. It is noted that fields on the flanks of the Montezuma area contain partial-retrograde condensate reservoirs and that heavy hydrocarbon components diminish in reservoirs at the basin margins. Nearly 90% of the recovered gas lies in fields located along major structural features including the largely stratigraphic Forbes and Winters plays. Structural trends appear to serve both as conduits for pervasive gas migration as well as the focus for the numerous structural and combination traps which account for most of the basin production to date.

Stratigraphic and structural relations of syntectonic sedimentary sequences associated with Cordilleran metamorphic core complexes provide valuable information about the style and timing of extensional deformation related to tectonic denudation. Adjacent to the Catalina core complex, the San Pedro trough and other nearby depocenters contain multiple tilted half-grabens of conglomeratic mid-Tertiary strata partly buried beneath Neogene basin fill. Major episodes of local geologic history included mid-Proterozoic construction of continental crust, subsequent but intermittent platform sedimentation extending through Paleozoic time, mid-Mesozoic initiation of arc magmatism that persisted at intervals through mid-Tertiary time, complex Laramide orogenic deformation of latest Cretaceous to early Tertiary age, and Cenozoic extensional deformation involving both mid-Tertiary and basin-range phases of development. Precambrian basement includes lower Proterozoic Pinal Schist intruded by voluminous lower to middle Proterozoic granitic plutons. Pre-Laramide stratigraphic cover includes middle Proterozoic sedimentary strata and intercalated diabase sills, Paleozoic carbonate and clastic units, and Mesozoic volcaniclastic and clastic successions. Laramide assemblages include metaluminous plutons and andesitic to rhyolitic volcanic fields, synorogenic nonmarine sedimentary sequences, and large bodies of peraluminous two-mica granite. Laramide structural features include both premetamorphic and ductile synmetamorphic thrusts within the Catalina core complex, brittle thrusts of uncertain vergence and overall configuration outside the Catalina core complex, and folds of varied geometry related in part to local thrusts exposed nearby. Paleogene erosion had stripped Laramide volcanic cover from wide areas by mid-Tertiary time. Migratory Tertiary arc magmatism within the intermountain region gave rise to diachronous polymodal igneous suites, represented within and near the Catalina core complex by extensive volcanic fields and local granitic plutons of late Oligocene age. Across the whole Southwest Border region, analogous mid-Tertiary igneous activity was succeeded, following an intra-Miocene tectonomagmatic transition, by basaltic to bimodal suites erupted during subsequent block faulting. Tertiary intermountain taphrogeny included a mid-Tertiary phase marked by listric or rotational normal faulting associated with tectonic denudation of core complexes along detachment systems, and a later basin-range phase of widespread block faulting. Mid-Tertiary extension was apparently promoted by reduction of interplate shear, kinematic rollback of a subducted slab, lateral spreading of overthickened crust, advective softening of arc lithosphere, and possibly by counterflow of asthenosphere. Basinrange extension was evidently initiated by shear coupling of Pacific and American lithosphere. The Catalina core complex displays characteristic geologic features: mylonitic fabric overprinted near a detachment fault by brecciation and chloritic alteration, a brittle detachment surface abruptly separating rock masses derived from different crustal levels, cover strata broken into multiple tilted fault blocks forming a shingled imbricate array, and surrounding syntectonic sedimentary sequences containing intercalated megabreccia horizons. The domical uplift that controls the exposed extent of the Catalina core complex apparently reflects isostatic upwarp of the midcrust in response to tectonic denudation, coupled with rollover arching above listric faults cutting beneath the core complex and with later uplift of crustal masses along steep block faults. A belt of mylonitic gneiss 10 km wide and 100 km long lies along the southwest flank of the Catalina core complex adjacent to the downdip segment of the detachment fault. Updip segments of the detachment system, across which cumulative displacement is estimated as 20 to 30 km, curve over and around the exposed core complex to merge with an inferred headwall rupture along the trend of the San Pedro trough. The detachment system probably involved a gently dipping aseismic slip surface beneath surficial tilted fault blocks; alternatively, faults now dipping gently may have originated as steep structures that rotated to shallow dips as slip proceeded. Field relations around the Catalina core complex are seemingly more compatible with the former interpretation, but insights gained from the alternate interpretation are useful for structural analysis of rotated tilt-blocks above the master detachment surface. Kinematic considerations imply that displacements within the local detachment system were diachronous during its evolution, but mylonitic deformation and detachment faulting both occurred during late Oligocene and early Miocene time. Tilted homoclines of syntectonic mid-Tertiary strata and less deformed beds of younger basin fill are both composed dominantly of alluvial fan and braidplain facies that grade laterally to finer-grained fluvial and lacustrine facies. Subordinate deposits include landslide megabreccia, algal limestone, lacustrine diatomite, and playa gypsum. The most voluminous strata are crudely bedded conglomerate and conglomeratic sandstone deposited by braided depositional systems. Clast imbrication is the most widespread and reliable paleocurrent indicator. Mid-Tertiary aggradation in half-graben basins gave rise to sedimentary onlap and overstep of evolving tilt-blocks, intricate local facies relations, and marked stratigraphic contrasts between sequences deposited within partly isolated subbasins. Stratigraphic successions that are concordant within basin depocenters are commonly broken by unconformities and intervals of nondeposition on basin flanks and across crests of bounding tilt-blocks. Mid-Tertiary strata exposed as tilted homoclines along the flanks of the San Pedro trough and across broad uplands north of the Catalina core complex are assigned to the following formations, each of which includes informal local members and facies: (a) Mineta Formation, mid-Oligocene redbeds including both conglomeratic fluvial and finer-grained lacustrine deposits; (b) Galiuro Volcanics, including lavas and domes, air-fall and ash-flow tuffs, and intercalated volcaniclastic strata of late Oligocene to earliest Miocene age; (c) Cloudburst Formation, also of late Oligocene and earliest Miocene age but including a sedimentary upper member of conglomeratic strata as well as a volcanic lower member correlative with part of the Galiuro Volcanics; and (d) San Manuel Formation, composed of lower Miocene alluvial fan and braidplain deposits that display contrasting clast assemblages in different areas of exposure. Generally correlative Oligocene-Miocene strata exposed south of the Catalina core complex are assigned to the Pantano Formation, which contains similar lithologic components. Less-deformed Neogene strata of post-mid-Miocene basin fill are assigned to the Quiburis Formation along the San Pedro trough, but stratigraphic equivalents elsewhere lack adequate nomenclature. High benchlands mantled by paleosols mark the highest levels of Neogene aggradation. Successive stages of subsequent erosional dissection are recorded by multiple terrace levels incised into basin fill. Key exposures of syntectonic mid-Tertiary sedimentary sequences in several local subareas reveal typical structural and stratigraphic relationships. Multiple fault blocks expose pre-Tertiary bedrock overlain by tilted mid-Tertiary strata confined to intervening half-grabens. Bounding syndepositional faults dip southwest and associated homo-clines dip northeast. Fanning dips and buttress unconformities reflect progressive tilt and burial of eroding fault blocks. Dips of block-bounding faults are inversely proportional to the ages of the faults. Steeper dips for younger faults suggest either progressive erosion of successive listric faults or progressive rotation of successive planar faults. Uniformly moderate to steep dihedral angles between fault surfaces and offset homoclinal bedding imply that the faults dipped more steeply near the surface when syntectonic mid-Tertiary strata were subhorizontal. Although the inference of listric faulting best links apparent strands of the Catalina detachment system, the alternate interpretation of rotational normal faulting is compatible with local structural relationships including tilt of porphyry copper orebodies. Within the San Pedro trough, multiple homoclines of mid-Tertiary strata are exposed locally in tilt-blocks exhumed by Neogene erosion from beneath nearly flat-lying basin fill of the Quiburis Formation. Faults bounding the mid-Tertiary exposures include backtilted strands of the Catalina detachment system, somewhat younger listric or rotational normal faults, and steeper basin-range normal faults that display offsets both synthetic and antithetic to the flanks of the San Petro trough. In Cienega Gap, flanking the Tucson Basin, multiple tilt-blocks of the Pantano Formation form part of the upper plate of the Catalina detachment system. Initial construction of alluvial fans by generally westward paleoflow was followed by ponding of lacustrine environments along the foot of secondary breakaway scarps that also generated massive megabreccia deposits. In summary, syntectonic Oligocene to Miocene sedimentation succeeded a prominent pulse of polymodal mid-Tertiary volcanism and was coeval with mylonitic deformation and detachment faulting along the flank of the Catalina core complex. The headwall rupture for the detachment system migrated westward from an initial position along the range front of the Galiuro Mountains. After mid-Miocene time, accumulation and subsequent dissection of essentially undeformed basin fill was accompanied by basin-range block faulting. The most challenging structural issue is whether fault strands of the Catalina detachment system are interconnected or are disconnected rotational segments.

ABSTRACT The structure and stratigraphy of the southeastern San Joaquin basin were reviewed for evidence that would document the impact on the basin of Miocene rotation of the adjacent Tehachapi and San Emigdio Mountains. Outcrops of basement rocks and volcanic intervals at the southeast margin of the basin contain paleomagnetic data indicating up to 59 degrees of clockwise rotation. The study used cross sections and maps of oil fields published by the California Division of Oil, Gas and Geothermal Resources. Information extracted included fault age and orientation, and stratigraphic data including gross unit thickness and net sand thickness. The geologic studies of the oil fields contain an abundance of evidence indicating Miocene extension. South of the Kern River, several fields contain numerous faults of early to middle Miocene age that generally fall on NW-SE or NE-SW trends. Fault offsets indicate a large amount of extension and correspond to the down-dropping of the floor of the Tejon embayment and break-up and collapse of the Edison high. Faults of similar age, present in fields north of the Kern River, have a slightly different NNW-SSE strike. Offsets on this latter set of faults are relatively minor and contributed in forming a wide shelf region. Sediments deposited during the middle and late Miocene reflect different styles of structural extension. South of the Kern River, the depositional gradient was very steep, and sand bodies representing deltaic, shallow-marine and deep marine environments are very localized in extent. North of the Kern River, sands deposited on the wide shelf are laterally extensive and represent deltaic and shallow-marine environments deposited at the terminus of a river system. The structural and depositional styles are similar between the Edison high and Tejon embayment area, indicating that the same structural events were responsible. The structural evidence is consistent with the rotation model of Goodman and Malin (1992) . However, if the Edison high block has rotated, then additional faults may be necessary to accommodate slippage against the adjacent Maricopa sub-basin block. The faulting style north of the Kern River is not consistent with rotation; thus rotation is likely limited to south of the Bakersfield arch.

Abstract The western portion of the Great Salt Lake contains two large Neogene basins, informally called the “North” and “South” basins. These basins are separated by an arch that trends northeast between Carrington Island and Fremont Island. Both basins are filled with Miocene, Pliocene, and Quaternary sediments and volcanic rocks. Each basin has an estimated maximum thickness of over 4300 m (14, 000 ft) of Tertiary rocks. Palynology indicates the oldest Tertiary sedimentary rocks present in both basins are Miocene, but a radiometric date indicates the presence of Oligocene rocks. Structurally, the basins are slightly asymmetric, deeper on the east with an obvious boundary fault zone on the east flank of each basin. Faulting is present on the western flanks but of a lesser magnitude. The most common structural traps found in these basins are anticlinal closures, faulted noses, and fault closures. These structures are probably the result of continued differential subsidence of pre-Miocene blocks throughout Neogene time. A total of 13 exploratory wells was drilled by Amoco in the Great Salt Lake, from June 1978 to December 1980, resulting in an oil discovery at West Rozel and oil and/or gas shows in eight other wildcat wells. The West Rozel oil field produces from fractured Pliocene basalts at a depth of 640-730 m (2100-2400 ft). The trap is a faulted, closed anticline covering approximately 2300 acres. The discovery well, Amoco No. 1 West Rozel Unit (NW NW Sec. 23, T8N, R8W, Box Elder County), has an oil column of 88 m (290 ft) but produced at rates of only 2-5 BOPH with a gas-lift system. The oil is 4° API gravity, 12. 5% sulfur, and has a pour point of 75°F. Two development wells that have smaller oil columns (No. 2, 26 m [85 ft]; No. 3, 60 m [194 ft]) were equipped with a downhole hydraulic pump and produced oil at rates up to 90 BOPH. Additional development of the field was not initiated because of the high water cut and the high cost of operating an “offshore” field.

Abstract The middle Eocene Tyee Formation was deposited in the Oregon Coast Range fore-arc basin (Figure 1). Heller and Ryberg (1983) and Ryu and Niem (1999) describe the Tyee Formation as part of a 6-km (3.7-mi)-thick package of sedimentary rocks that rests unconformably on the Paleocene Siletz River Volcanics (Figure 2). The Umpqua Arch (Figure 1) appears to have influenced deposition of the Tyee and divided the basin into two sub basins. Field mapping by chan and Dott (1983) and Heller and Dickinson (1985) suggests that the Tyee depositonal system includes fluvial and deltaic deposits to the south and that this system prograded to the north through time. Outcrops of the middle Eocene Tyee Formation along Highway 20, west of Corvallis, Oregon, display facies that are characteristic of the distal end of a sand-rich basin-floor fan. This area is more than 100 km (60 mi) basinward of slope and deltaic deposits of the Tyee Formation (Figures 1 and 3). A series of road cuts along Highway 20 exposes up to 460 m (1500 ft) of strike section that shows no evidence of channelization (Figure 4). The primary sedimentary facies here are relatively thick (1-3 m [3-10 ft]) beds of massive sandstones (Ta). These beds are, in many cases, capped by thin (0.2-0.6-m [0.7-2.0-ft]-thick) beds of organic-rich, muddy, fine-grained sandstones that contain rip-up clasts (Figures 5 - 7). We interpreted these muddy beds as slurry deposits (sensu Lowe and Guy, 2000), that is, deposits that record a flow transitional between turbidity currents and debris flows.