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We determine the paleoelevation of the northern Sierra Nevada (California) in the Oligocene based on hydrogen stable isotope compositions of meteoric water preserved within volcanic glass from ignimbrites sampled across the range. A 48‰ decrease in the isotopic composition of hydrated glass from ignimbrites located near paleosea level to ignimbrites 100 km to the east refl ects the effect of ancient high topography on precipitation. These data show that 31-28 Ma ago, the northern Sierra Nevada had a steep western gradient and elevations similar to the present. This study, placed in the context of other paleoaltimetry studies, suggests that the range was a high topographic feature throughout the Cenozoic and that the majority of uplift occurred in the Late Cretaceous to early Cenozoic, much earlier than some studies have proposed.

Records of past topography connect Earth's deep interior to the surface, reflecting the distribution of heat and mass, past crustal structure, and plate interactions. Many tectonic reconstructions of the North American Cordillera suggest the presence of an Altiplano-like plateau in the location of the modern Basin and Range, with conflicting timing and mechanisms for the onset of surface-lowering extension and orogen collapse. Here we show, through a paleotopographic profile, that from the Eocene to the Oligocene a high, broad orogen stretched across Nevada, with a distinct crest that divided a continuous westward-draining slope extending to central California from an internally drained eastern Nevada plateau. This paleo-orogen maintained demonstrably higher-than-modern elevations, reaching 3500 m in the late Oligocene. Despite the long-term high gravitational potential energy of the crust supporting this topography, surfacelowering extension did not occur until the transition to a transform margin changed the external kinematic framework of the system. Maximum surface lowering was spatially decoupled from brittle upper crustal extension, requiring a large component of mid-crustal flow.

Slab rollback processes alter the intraplate force balance and buoyancy of the overriding plate, driving surface uplift or extension. From ca. 55-24 Ma, Farallon slab rollback produced migrating volcanism and sedimentation across the western United States as stress on the North American plate transitioned from subduction-driven compression to widespread extension. Hypotheses regarding rollback-driven surface deformation differ widely in timing and magnitude. Here we combine hydrogen isotope ratios with high-resolution geochronology to show that a high-elevation plateau extended westward from the Sevier-Laramide fold-thrust belt across Utah and eastern Nevada prior to slab rollback. Quantitative paleoelevation estimates show that this plateau had obtained over 80% of peak paleoelevations by middle Eocene. Slab rollback, heating, and lithospheric delamination generated 400-600 m of Oligocene surface uplift. Concurrent extension limited overall uplift and rollback-induced mantle flow likely contributed to the propagation of upper crustal extension that formed the Basin and Range province.Plain Language Summary Changes in surface elevations are critical to understanding the formation and evolution of mountains and basins across ancient landscapes. Slab rollback-retreat and steepening of the downgoing tectonic plate during subduction-can transform Earth's surface by altering the stresses on the overriding plate. By measuring the ratios of hydrogen isotopes in ancient rainwater, preserved for millions of years in volcanic ash, we can estimate past elevations. Here we measure past elevations across the Basin and Range province of Utah and Nevada to reconstruct topography before and during slab rollback. Results show that a high elevation plateau extended westward from the western edge of the Rocky Mountains across Utah and eastern Nevada prior to slab rollback. Slab rollback generated a shortlived interval of 400-600 m of surface uplift, much less than has been previously estimated. Instead, subsequent processes resulting from rollback likely contributed to collapse of the high plateau and the widespread extensional faulting that created the characteristic topography of the modern Basin and Range province.