Petrographic, conglomerate and detrital-zircon analyses of formations in southern California can determine consanguineous petrofacies and lithofacies that help constrain paleotectonic and paleogeographic reconstructions of the southwestern United States. Arkosic sandstone of the lower Middle Miocene Cajon Valley formation is exposed on the southwest edge of the Mojave block and juxtaposed against Mesozoic and Paleozoic rocks by the San Andreas fault (SAf). Early work in Cajon Valley referred to the formation as Punchbowl, due to its similar appearance to the Punchbowl Formation at Devil's Punchbowl (northwest along the SAf). However, paleontological work placed Cajon Valley strata in the Hemingfordian-Barstovian (18-14 Ma), as opposed to the Clarendonian-Hemphillian (13-9 Ma) Punchbowl Formation. Since the Cajon Valley formation was deposited prior to being truncated by the San Andreas fault, the 2400m-thick, laterally extensive subaerial deposits likely were deposited across what is now the fault trace. Restoring 310 km of dextral slip on the SAf system should indicate the location of offset equivalent sandstone. Restoration of slip on the SAf system places Cajon Valley adjacent to the Caliente and La Panza Ranges, east of San Luis Obispo. Although analysis of detrital zircon from Cenozoic sandstone throughout southern California has been crucial in establishing paleodrainage areas, detrital zircon from the Cajon Valley and equivalent formations had not been analyzed prior to this study.

Paleocurrents measured throughout the Cajon Valley formation indicate a source to the NE, in the Mojave Desert. Sandstone samples analyzed in thin section using the Gazzi-Dickinson method of point-counting are homogeneously arkosic, with slight compositional variability, making differentiation of the Cajon Valley formation and potential offset equivalents problematic. However, Branch Canyon Sandstone and Santa Margarita Formation samples are compositionally the best match for the Cajon Valley formation.

Detrital-zircon ages were determined from the Cajon Valley formation and related strata. These data are slightly more variable than sandstone composition, with distinct age peaks at 85-90 Ma, 150 Ma and 250 Ma. These ages correlate with batholiths in the SW Mojave Desert. Of the nine samples from six formations collected as potential offset equivalents, Branch Canyon and Santa Margarita samples are most similar to Cajon Valley samples, in terms of both detrital-zircon ages and sandstone composition.

Based on 310km of post-Miocene offset on the San Andreas fault system, the Cajon Valley formation restores adjacent to shallow-marine sandstone of the Santa Margarita Formation and Branch Canyon Sandstone Member of the Monterey Formation in the Caliente and La Panza ranges. Cajon Valley sandstone is interpreted to represent a Miocene fluvial system on a coastal plain, flowing toward a delta on a narrow continental shelf.

The Middle Miocene Mint Canyon and Caliente formations represent sedimentation after triple-junction extension in southern California. Sandstone and conglomerate petrology, combined with detrital-zircon analysis, determines provenance of the Mint Canyon and Caliente formations. These data indicate that most detritus is locally derived, rather than being derived from the Chocolate Mountains across the San Andreas fault. The Mint Canyon and Caliente formations received Proterozoic anorthosite-syenite-gabbro and Triassic Lowe plutonic detritus from the San Gabriel Mountains throughout their depositional history, but show variations geographically from more locally derived sources, including Pelona Schist from Sierra Pelona.

Discriminant analysis of sandstone and conglomerate indicates strong correlation between the Mint Canyon and Caliente formations. Each group for the Mint Canyon Formation (schist (S), volcanic (V) and plutonic (P)) shows a distinct age peak (based on detrital zircons) from a nearby source rock. The plutonic group has a strong Lowe Pluton signal (220 Ma), the volcanic group has a strong Vasquez and related volcanics signal (25 Ma) and the schist group has a strong Lowe Pluton and Pelona Schist signal (220 Ma and 75 Ma). The Caliente Formation is less distinctive, but shows the same Lowe Pluton (220 Ma), unknown local plutons (150 Ma), volcanic (25 Ma) and schist (75 Ma) signals. All samples show Proterozoic anorthosite-syenite-gabbro and gneiss signals (1200 Ma and 1700 Ma) that are weaker to the west.

This study supports the importance of integrated multi-method analyses. Conglomerate petrology, sandstone petrology and detrital-zircon analysis constrain drainage styles of Mint Canyon and Caliente provenance. Independently, each method provides limited provenance information about rock type or age, but together, they demonstrate correlation between the Mint Canyon and Caliente formations, and refine our understanding of source rocks and paleogeography.

The Vincent Gap region of the eastern San Gabriel Mountains in southern California is a small but important piece of an originally continuous terrane separated into the Tejon, Soledad and Orocopia regions by the San Andreas fault system. The middle-upper Miocene Punchbowl Formation has been considered the oldest Neogene strata of the Vincent Gap region. The present study documents that strata southeast of the main exposure of the Punchbowl Formation, though aerially restricted, are temporally extensive; together with the Punchbowl Formation, they comprise a sedimentary record that spans from ~25 to ~6 Ma, includes equivalents of the Vasquez, Tick Canyon and Mint Canyon formations of the Soledad region, and relates to three sequential tectonic stages in southern California. Uppermost Oligocene-lower Miocene strata are closely correlative with the Plush Ranch, Vasquez and Diligencia formations of the Tejon, Soledad and Orocopia regions, respectively; they formed during extension induced by triple-junction instability. Interbedded 25 Ma volcanics near the base of these strata are chemically and chronologically similar to those of the Plush Ranch, Vasquez and Diligencia formations. Middle Miocene strata beneath the Punchbowl Formation are equivalent to the Tick Canyon Formation of the Soledad region, and document exhumation of the Pelona Schist. Sandstone petrofacies, conglomerate composition and detrital-zircon age data provide compatible but distinct provenance information; using all three in combination results in a more complete understanding of the provenance of each of these units. The results of this study imply that transrotation of the western Transverse Ranges and accompanying basement exhumation extended farther inboard than generally thought, adjacent to if not across the future trace of the San Andreas fault. Data from the Vincent Gap also reveal that the middle-upper Miocene Punchbowl Formation was likely part of a large drainage system, with the Mint Canyon Formation of the Soledad region representing a tributary of this system that joined downstream, and the Caliente Formation of the Tejon region representing the confluence of the two.

The San Gabriel Mountains of southern California contain anticlinoria of schist thought to correlate with one another, and with the Chocolate Mountains anticlinorium to the east. These correlations provide cumulative-slip estimates for the Punchbowl and southern San Andreas faults, respectively; however, the validity of these correlations, as well as the original orientations of these anticlinoria, is debated. This dissertation presents four related studies, each addressing a different aspect of this problem. Chapter 1 presents sedimentologic and structural data verifying that the two anticlinoria of the San Gabriel Mountains were continuous prior to 40-50 km of dextral slip on the Punchbowl fault, and casting doubt on the 80-110 km of dextral slip on the San Francisquito-Fenner-Clemens Well fault suggested by some prior studies. Chapter 2 presents structural data from the schist of the larger anticlinorium of the San Gabriel Mountains, which supports its correlation with the Chocolate Mountains anticlinorium, and thus estimates of approximately 240 km of dextral slip on the southern San Andreas fault. New data are combined with previously published structural and paleomagnetic data, which have been interpreted as implying different architectures for the anticlinorium, suggesting a model reconciling the datasets, and implying an originally linear, approximately northeast/southwest trend of the anticlinorium. Chapter 3 proposes a strain-partitioning model for the anomalously oriented Mojave segment of the southern San Andreas fault, in which slip south of this segment is partitioned within this segment into a strike-slip component along the San Andreas fault itself, and a shortening component beside it. This model, together with a previous study’s insight, brings otherwise contradictory cumulative-slip estimates of approximately 240 km and 160 km for the southern San Andreas fault into agreement. Chapter 4 presents new fault-kinematic data, and sequential reconstructions of the San Gabriel block as maps and cross sections, suggesting that the anticlinorium is in the hanging wall of a detachment fault, rather than the exhumed footwall as previously suggested. New geochronologic and geochemical data support correlation of the anticlinoria and constrain the onset of extension to ca. 26-25 Ma.

The Sierra Nevada of California represents the roots of a long-lived magmatic arc (primarily Cretaceous) that is presently being dissected as the range is uplifted, beginning in the south and progressing northward. This dissection is occurring concurrently with northward migration of the Mendocino triple junction, south of which magmatic-arc activity is absent, and north of which magmatic-arc activity continues. A north-to-south transect along the Sierra Nevada represents transitions of active magmatic arc to transitional arc to dissected arc, and in the southern Sierra Nevada, to uplifted basement. Thus, analysis of composition of modern sand derived from these separate parts of the Sierra Nevada provides a test for actualistic sand(stone) petrofacies of magmatic arcs at all stages of dissection.

Rigorous statistical analysis of the composition of modern sand from the Sierra Nevada characterizes stages of magmatic-arc dissection. Discriminant analysis of point-count data from Sierra Nevada modern sand defines four compositional groups and distinguishes clearly between undissected-arc and uplifted-basement end members. Two intermediate compositional groups reflect the complex geologic history of the Sierra Nevada. Volcanic and plutonic rocks dominate one intermediate group; metamorphic and plutonic rocks dominate the other. The former group exhibits characteristics of Dickinson's (1985) "transitional are," whereas the latter is equivalent to "dissected arc." No single compositional parameter is diagnostic of the degree of magmatic-arc dissection, although volcanic-lithic content clearly differentiates between "undissected" and "basement" groups. Regional compositional trends are evident when recalculated point- count data are plotted against latitude.

Sand composition in the southern Sierra Nevada reflects significant Cenozoic uplift of the batholith, resulting from Basin and Range extension. High concentrations of quartz and feldspar, and extreme lithic depletion are typical at the southernmost Sierra Nevada; this extreme depletion characterizes "basement uplift."

The primary drainage divide of the Sierra Nevada forms a rough compositional boundary between eastern and western groups. Potassium-feldspar content best distinguishes these groups, with higher values in the east.

Rigorous confidence regions in ternary diagrams yield results that are similar, but not identical, to hexagonal fields of compositional variation. Arithmetic means, associated with hexagonal fields, are not identical to geometric means, associated with logratio confidence regions. Definition of sand(stone) provenance groups, in general, depends on both data-acquisition methods (e.g., Gazzi-Dickinson method) and statistical methods (e.g., Weltje method), so that direct comparison of data analyzed using different methods is unwarranted.