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The Lobo Formation consists of intermontane lacustrine or palustrine, fluvial, and alluvial-fan deposits. The Lobo near Capitol Dome in the Florida Mountains of southwestern New Mexico is about 116 m thick and consists of a basal pebble and cobble conglomerate containing locally derived carbonate clasts, overlain by very fine to fine-grained sandstone, reddish-brown siltstone and pebbly sandstone, and an upper cobble and boulder conglomerate with basement clasts.

In the Victorio Mountains, the Lobo is an upward-fining succession (~325 m thick) composed of alluvial-fan and fluvial deposits. Sediment accumulation slows in the latter half of Lobo deposition as indicated by paleosols in the upper half of the Victorios section; depositional style and paleosols indicate deposition in arid conditions. Basal conglomerate clasts have been derived from diverse sources: a Proterozoic basement, Paleozoic carbonate and siliciclastic strata, Jurassic basalt flows, and Lower Cretaceous strata (Bisbee basin). The Lobo “super-sol,” a paleosol carbonate, is present along a karstic paleosurface at the base of the Lobo in the Florida Mountains section. δ18O values of this carbonate range around -12‰, suggesting a paleo-elevation of ~2400 m above sea level.

The Victorio Mountains contain paleosols approximately 140 m up section that have carbonate values that range around -16‰, suggesting a paleo-elevation of about 3500 m above sea level. Preliminary paleomagnetic analysis indicates four brief normal intervals among a mostly reversed section; data suggest deposition occurred between 64 and 51 Ma followed by a post-depositional clockwise rotation of 25-30° about a vertical axis. Lobo data correspond well with the proposed Hot Springs Fault System, which suggests an offset by a dextral strike-slip system of approximately 26 km; this system’s location and displacement is sufficient for our suggested rotation given it occurred post-Lobo time.

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