Differential Tectonic Uplift of the Watersheds in the Santa Rosalia Basin, Baja California Sur, Mexico.

The Santa Rosalia Basin (SRB), in the Baja California peninsula, Mexico, is related to the transtensional rifting of the Gulf of California and shows evidence for being tectonically active during the Pleistocene. It has characteristic sequences of non-symmetrical Pleistocene fluvial and marine terraces and remarkable stream incision. This study analyzes the watersheds in the SRB and relates them to the spatial variation of geomorphic indices and marine-fluvial terraces, in order to identify a differential tectonic deformation. Six to seven different terrace levels were identified along the Boleo, Purgatorio, and Santa Agueda arroyos, supported by measurements using RTK-GPS, which were linked to soil chronosequences profiles and luminescence dating. Geomorphic indices; hypsometric integral (Hi), asymmetry factor (AF), and transverse topographic symmetry factor (T), were to obtained using GIS. Watershed hypsometric curves show a southward increase of watershed maturity in the arroyos of the SRB. The AF displays variation of 33.5% for Arroyo Boleo, 36.23% for arroyo Purgatorio, and 55.09% for Arroyo Santa Agueda, suggesting a southward increasing in the watershed tilting across SRB. The average of TS for each watershed is consistent with the southward variation of the AF index, values of TS varies from 0.42, 0.33 to 0.23 (Arroyo Boleo, Arroyo Purgatorio, and Arroyo Santa Agueda, respectively). The height of terrace at segments of 3, 5 and 7 km range from ~6 to 50 m showing a consistent elevation difference of the terrace surfaces in the watersheds support the values of geomorphic indices. Correlation of geomorphic indices and fluvial geomorphology elements of the SRB indicates a possible influence of a differential tectonic uplift towards La Reforma Caldera, displaying a southward tilting of the watersheds.