STRATIGRAPHIC INTERPRETATIONS AND PROVENANCE OF THE MID-TERTIARY SOLEDAD ROJO FORMATION OF THE LOWER COLORADO RIVER EXTENSIONAL CORRIDOR, WESTERN PALO VERDE MOUNTAINS, SOUTHEASTERN CALIFORNIA

New stratigraphic and paleocurrent data from the Soledad Rojo formation, a red conglomerate and sandstone unit in the western Palo Verde Mountains, southeastern California, illustrate the evolution of a basin that was formed during Mid-Tertiary crustal extension. The Soledad Rojo formation is subdivided into three distinct subunits of variable lithofacies and clast compositions that display changes in sediment provenance and depositional environments during the history of the basin. Preliminary stratigraphic and structural interpretations infer that deposition of te formation occurred in a synextensional basin of a moderate energy alluvial/fluvial system derived from nearby sediment sources. Conglomerates within the Soledad Rojo formation subunits were likely derived from local mountain regions due to the large grain sizes, subangular to subrounded textures, volcanic and metaplutonic clast compositions in an arkosic matrix, all which suggest a relatively short distance of travel after erosion occurred. Paleocurrent analysis, thin section point-counting, and clast count data further suggests that the Soledad Rojo formation was derived from local exposures, with clast imbrications suggesting NW/NE paleoflow directions. Though the timing and deposition of the three subunits in the Soledad Rojo formation is difficult to constrain, recent ⁴⁰Ar/³⁹Ar and detrital zircon U-Pb geochronological dating in the basin indicates the red-bed unit was deposited during the late Oligocene to early Miocene (ca. 23.5 to 25 Ma). Further research of this region will help in the direct identification of the source(s) for the sediments entering the basin, identify the tectonic framework that may have contributed to the depositional environment, as well as determine if previous regional stratigraphic correlations and interpretations are valid.